How do you not get exhausted?

Start easy and slow. Give up fries and soda. Eat grilled not fries. Eat a salad with junk. A salad first with chips. You can do it. Small steps equal big changes. Focus on the positive and work up gradually to a routine

Only way you're going to do it is to just do it and keep doing it. Might be harsh, but that's it.

Most people feel energised so if not, maybe you're not getting enough calories and/or sleep?

I completely understand. I find that, for me, specificity is essential. So my objectives for important projects (like weight management) are set using the SMART criteria:

Specific – target a specific area for improvement.
Measurable – if you can't measure it, you can't manage it. Doesn't have to be a number.
Attainable – be realistically able to achieve it. " I'll be an Olympian" is not exactly attainable for most of us.
Relevant – Important to you. It will not matter to me if I ever write a song or have a nice yard with flowers.
Time-related – specify when the result(s) can be achieved. "by July, by 2015,", etc.

Signing up for races (you can walk part of them if needed) is a huge motivator for me as well. I chose one far enough away that it was feasible I could run the whole thing. So in Feb this year (at 257 lbs) I chose one to try for coming up in September. Then I started a 12 week walking plan to prepare for the 9 week couch 2 5 k program ( which I will finish in June). I then will be able to run 30 min, but prob not a whole 5k. I then have a few more months to build my running time. So, my point, pick your big goal and set little goals to reach it. Each progression I make I really celebrate bc I know I'm getting there. Even my 5k goal is a step towards my REALLY big goal of losing 127 pounds. But for me that amount is too overwhelming. Motivation or willpower comes and goes, so having a plan really helps.

NOW I can't figure out what it is. It happened to me last week but I fell of the wagon just one week after I began and gained the weight back because I'd been eating horribly for two weeks before my motivation kick started again.

I don't understand the cause of this cycle and I know it has to do with lack of will, I just don't know how to get that will power. How do you do this long term?

[1] Watching what I eat. Food is fuel, and you can't expect repeated good performance when you're shoveling garbage into your gas tank. I set my calories and go to it - worrying less about the daily fluctuations of my calorie intake and concentrating more on the weekly total. It gives me a lot of flexibility.

[2] Exercise is damned important. It can't be bolted onto the day as a "when I have time I'll go for a walk" - it MUST be integrated into your day in ways that will build it into an immutable habit. I'm lucky (?) in this way because I have an hour between when my work-day ends and the train I take home leaves the station; it's a two mile walk that I've been able to slow-jog in under 25 minutes.

[3] REST. Get good sleep. No noise, no light, turn off computers and bright lights an hour before bed, and so on. My personal feeling is if you're not getting solid rest nothing else seems to work right.

[4] Set goals and milestones. My original plan was to get to a normal weight for my height, which required me to drop seventy-three pounds, from two hundred thirty to one hundred fifty-six. Looking at it all at once was daunting. Setting easily met milestones along the way - lost five pounds, lost ten, lost 5% of my body weight, walking three miles an hour, walk a mile all in one go - kept the motivation to succeed moving forward.

[5] Let them become habit. I can't count how many times thinking "I'm too tired for this. I can't do the walk today" only to find my feet under me and leaving for a two-mile wander to the train. The doubts in my head were being overridden by the good habit of moving when I could, whether I felt like it or not. Little by little, that part of my head that caused me to doubt my own abilities died of neglect.

[6] ACCEPT THAT YOU'LL SCREW UP. Everyone else screw it up, what makes you think you won't? I see so many people with the mindset of "Well, I had a cheeseburger for lunch, this day is shot" and proceed to devour another three thousand calories of the worst crap imaginable. That's equivalent to getting into a minor fender-scrape and then deliberately driving the car into a telephone pole. It's a loser's mindset.

When bad things happen - whether you've caused them by your behavior or not - SALVAGE THE REST OF THE DAY. Use the mistakes as lessons of behaviors and things to avoid. If you go over on your calories, cut back the next day, or several days, if need be to keep the weekly total close.

[7] Keep going. The scale is not your enemy. Scale progress will stall for the best of reasons as well as no discernible reason at all. I had one stall that lasted six weeks only to finally have eight pounds drop all at once. I've no idea why it happened. It the end, the stalls made no difference - over the eighteen months it took be to safely drop seventy-three pounds I averaged overall about a pound a week.

tl;dr: Set measurable goals, set a lot of waypoints, be S.M.A.R.T. as tycho_mx said.

For me?

My philosophy has been that just about everything in life is a choice, and that what we are at any given time is the sum total of those choices.

I chose not to take good care of myself for years & its how I got to 312 lbs. I accept the responsibilities and results that came with the choice.

I've now chosen to see this as a lifestyle change & I accept the responsibilities and results of that as well.

I have found that this direct honesty with myself in both cases serves as all the motivation I need. If I want results, only I can make the choices that will influence those results, whether positive or negative.

In short, its about what you truly want & the choices you will make to get there.....

And as another poster eloquently said? Accept that youre going to screw up. Nobody's perfect.

if you're feeling exhausted, then that's sometimes a sign you're not eating enough calories.... if you're falling off the wagon and getting the urge to binge after such a short time, my first question is........... is your calorie goal high enough? If it's not, then it's like asking your mechanic why your car stops running halfway through the journey when you're not putting enough fuel in it.

Reasses your calorie goals. Aim for slow fat loss, and aim to make your diet as easy as possible to stick to. Make your exercise programme something you really enjoy and will find it easy to stick to. A lot of people are in a "self-punishment" mentality and/or an 100% or nothing mentality, whereby they think they have to do everything to the max, punish their bodies to the max, and if they slip a little bit then they're a loser and may as well give up........ well that's a really terrible mentality to be in for long term success at fat loss. The goal is to be healthier and leaner, not to win an olympic gold medal. There's absolutely no need to punish yourself, deprive yourself or torture yourself, and this 100% or nothing mentality is very counterproductive. Instead, understand that for successful fat loss you need a calorie deficit, and for health and good body composition you need exercise/physical activity and a balanced diet. That is it. Anything more than that is overkill. (yep you need more than that if you want to win contests at a sport... but that's a totally different goal to fat loss!).......... so, find ways that are easy to stick to, that will give you a calorie deficit, keep you physically active, and a balanced diet. You can get a balanced diet while still enjoying food like McDonalds or whatever food(s) it is that make you fall off the wagon... just make sure that the rest of your diet is balanced and that you're not going over your daily calorie goal. There's no benefit to losing weight quickly, in fact it's counterproductive for long term success, so set yourself a modest calorie goal of 0.5-1lb weight loss a week, and eat all your calories, and eat back 80% of your exercise calories. This gives you room to enjoy all the foods you want to AND still get a balanced diet by including foods rich in protein, fibre, vitamins, minerals and essential fatty acids as well. Pick a form of exercise that you really enjoy and is convenient to fit into your day on a regular basis........ then give yourself a goal to stick to it long term, e.g. 1 week goal, 3 week goal, 2 month goal, etc. Focus on complying with this, i.e. success is sticking to the plan for x weeks/months, not how much fat you lose. Then, over time, the fat may not come off so quickly, but it will come off easily, as you've set yourself up to succeed while enjoying your new, healthier lifestyle. And you shouldn't end up feeling exhausted either, this way of losing fat results in high energy levels (because the deficit is small and nutrition is good and exercise makes you feel energised).

That's it really... fat loss is not a competition or a race... an all or nothing attitude is very counterproductive, instead you just need to be good enough, and you need to really enjoy the new lifestyle that's going to get you there and keep you there (because if you revert back to the old ways, then you'll regain the weight).