Can't seem to stick to one plan...

Tawniey

Hello all.
This is my first time posting a topic, and I hope you all can help me!

Alright, here's my situation--
6 years ago, I was so overweight and in such denial of it that I refused to even look at a scale for fear that it would shock me into reality. Back then, while I exercised for 3-4 hours a day, I would eat insane portions of foods that are considered bad for you in small portions, and drinking 2 or more bottles of soda per day.
When I got to college two years ago and realized that even my size 20 pants were getting tight, I finally woke up. I realized I had to do something. So, I cut back drastically on portions, but my exercise rate also fell dramatically that year. By the time I comfortably fit in a size 18, and my bra band size had dropped from a 44 to a 40, I felt confident enough to get on a scale. At that point I was 248 lbs.
The next thing I tried was the 17 day diet on cycle 1. I then shrunk to a size 16 in pants and a bra band size of 38, and made my way down to 230lbs. However, since I was limited to my dormitory's food, I rebounded from that pretty quickly. There were only so many days in a row that I could eat nothing but grilled chicken breast in hot sauce and a dry salad.
So, I stopped with the 17 day diet and picked up more active exercise. My portions slowly grew back to carb-heavy over-eating (though not as bad as they were before I started trying to lose weight). The exercise helped to slow the weight return.
Then I stopped exercising again and the weight came back on fast. Events had made me depressed and food once again became a comfort.

So I've started trying to keep track of calories here to get back on track. I'm now 250lbs again, and still I refuse to go back to the sizes I've shrunk out of.
After finally recovering from an injury that's plagued me since February, the last two days I've been getting back to an exercise schedule, and I'm working on cutting calories again.

Here's where I need your help--

Firstly, I'm worried that I'll burn myself out on another lifestyle change attempt, because every time I try to change, I bounce back to my old habits after a month or so. Does anyone have any recommendations to avoid a burnout?

Next, when I work out, I work out HARD. I get up into the 80-95% heart rate zone simply to keep from feeling bored while working out. I play outdoor games in extreme competitive-mode. I swordfight, and can typically lift more than your average 20-year-old girl.
It's almost all-or-nothing the way my energy levels get. If I work out hard, I get energy to keep doing so, as long as I can make it past the initial push. But when I let myself rest, I get tired and can't find a way to force myself to do anything but walk down the street to go to class.
Also, working out more tends to make me hungrier, even later in the week after a big workout. And eating more food contributes to the tiredness that makes me stop working out.

I know I must be doing something wrong, since I keep burning myself out on these attempts. Even when I manage to stay plateaued at a weight, I yo-yo in energy levels as I try to find a healthy lifestyle.
The only things that have managed to stick with me are my initially reduced portions and my reduction of soda from 2 20oz bottles per day to 1-2 12oz cans per week.

Sorry that this is a big, long, wall of text. Hopefully some of you might have some advice for my situation.

Thanks in advance!