Scary sudden weight gain despite exercise that worked before

It sounds like your job has turned you into a workaholic, which is a form of adrenalin addiction. You've carried that stress into your vacation and exercise program. You've made your vacation a "job". When these methods were working better for you a few years ago, were you getting better sleep? Were you worrying less? I would add something more relaxing into your exercise mix... Tai Chi or very mild stretching or very light yoga with a teacher who understands your injuries. Relax. Breathe. Take at least one complete rest day each week. Alternate light, moderate, and heavy workouts during the rest of the week. Use more of your vacation to recover from sleep deprivation. A lack of sleep makes it very hard to lose weight. Check out Jeff Galloway's approach to training... the way he alternates the intensity of workouts. As you get older, rest days and light exercise days are more and more important.

Hard exercise after a period of being sedentary will usually add weight as you build back your muscles. In this case, it is most likely water retention. You seem to be drinking way too much water, but given that you are maybe overdoing the exercise, you may crave it. I agree with the feedback one other person gave... you are on vacation, maybe eating out more and getting more salt. Cut out salt (almost impossible in restaurants) and you will begin to release the water.

I would check out the principles behind the Fat Flush Diet developed by Ann Louise Gittleman. She once worked for Pritikin, then wrote a book called Beyond Pritikin, that established the need for healthy fats and oils. I liked her early book before her methods became an industry. However, her thinking tends to develop with the latest research, so she's worth studying a bit. Is your diet low fat more than focusing on getting healthy oils? If you are not getting healthy oils and you are focusing on a low fat approach, you body might think it's starving and it will hold on to whatever it gets. A lack of healthy oils will influence moods, disrupt sleep, dry the skin, hurt the joints, etc. Your body will also tend to retrain whatever bad fats you do eat. Gittleman's very effective 2 week fat flush program is often criticized as not being about losing fat but more about losing water weight. That's actually one of its virtues. If, for a short period (two weeks only), you avoid the starchy carbs, eat healthy vegetables, lean meats, some salmon, fruits in moderation, get the right oils (daily borage, fish, flax oil), and get plenty of sleep, then your body will turn into a fat burning machine. You will also get rid of unneeded water. For two weeks, you can drop a pound or two a day, and most of it will probably be water weight. She also recommends cranwater for the kidneys. Unsweetened Cranberry Juice in a ratio of one cup of juice to 7 cups of water. With lemon added to the glass, it's a deliciously refreshing drink for these hot summer days. Drink two quarts of that mix each day for a couple of weeks. Your kidneys will enjoy it. When the body chemistry goes wacky, we tend to retain more water than we need. I'm not out to push a specific plan here, but most current research is tending to head in this direction. However, don't overdue any of this...

And... the main through-line in all the great advice you've gotten here... RELAX ! Stop worrying ! Drop the stress !

Here are the words of an old Paiute to the LA worker bees that would visit him in the Eastern Sierras... "Sit down and make yourself useless!"

Your life has changed, and you probably don't have time to walk 9 miles a day most of the time. The good news is that since you're working, you can afford a bicycle, a gym membership, time at a swimming pool, whatever works best for you. You can get in a good workout in 30-60 minutes a day.

But what worries me is that in the past, no matter how much fat I gained, I was literally able to get rid of it within just a few DAYS of long distance walking. I think I am no more able to do that now.

No one can get rid of all the fat they've gained within a few days. I guarantee that it didn't happen like that in the past, even if it seemed so. I would bet you perceived that incorrectly, and that has led to unreasonable expectations, sending you into a panic when it doesn't happen. So don't worry, it sounds like you're totally normal.

Can you bring your own healthy foods to work?
How much exercise can you get on your breaks?

4L of water literally weighs 4kgs

Keep drinking & try to stop worrying. Take things sloooooooowly. I've been on this 'journey' for 21mths now and i still haven't reached the end (I know I never will as it's a forever commitment) but I sure as hell feel a heck of a lot better than I did 2yrs ago.
I've also been stuck/plateaud (there's no such word but ykwim lol) for 6 months - yes SIX months - but I haven't given up. I just keep on keeping on hoping that some time soon things will start moving again.

This weightloss/healthy living thing is definitely a game of patience. You can do it.

Yes, if and I stress the word "if", you want it enough to do what it takes to have both a successful career and a healthy life style it can be done. You might have to slow the track you are on some at work to do it but given your age you can still meet all of your goals both in your career and in your health. In fact focusing on reaching your health goals can improve your functioning and further your career path at work.

Keep in mind that with the changes in your life i.e. leaving school for a career, injury, a more sedentary lifestyle. Are not the only things that can affect your ability to lose weight. The stress of a fast track career can do that as well. Stress can cause all kinds of problems including one of the biggest is that if you are distracted by stressors you may be eating more than you realize. Stress hormones can also play havoc. Try adding 20 min a day of purposeful relaxation to your routine. For example, I lose far more weight and feel better when I compensate for a high stress work week by adding a 20 minute soak in the hot tub after a swim or workout.

Thanks again!

Regarding calories tracking...

Well, I actually started doing it once very seriously, my "excuse" to stop doing it regularly was that there is so much food where you cannot actually find the calorie count.

In supermarkets, you can always find it on the label, but in a restaurant not. Even if I cooked my own food, I could only guess, right?

Or is there a guide on how to calculate calories for food that you make or eat at restaurants?

In a restaurant it can be hard. You get better at estimating the calories in restaurant food when you have estimated the calories in your own cooked meals a lot, and learned about portion sizes and stuff. Personally I don't go out to eat much and when I do I try to compensate with exercise. It seems to work.

Estimating calories in your own cooked food is simple, you just weigh all the ingredients and count the calories for it. If you have standard recipes for certain meals you eat often you can even save the recipes in myfitnesspal.

Thanks again!

Regarding calories tracking...

Well, I actually started doing it once very seriously, my "excuse" to stop doing it regularly was that there is so much food where you cannot actually find the calorie count.

In supermarkets, you can always find it on the label, but in a restaurant not. Even if I cooked my own food, I could only guess, right?

Or is there a guide on how to calculate calories for food that you make or eat at restaurants?

For food that you make, MFP has a recipe tool. It's under the food tab, then recipes. You enter in all the ingredients and how many servings it makes, and it give you calories and nutritional value, and you can even save it for future use.

Many restaurants have nutritional values online (and for those that don't, other websites like Livestrong have estimates). A lot are also already entered into the database on MFP. And if it's not there, you can find something close (for example, a local chain, Village Inn, doesn't have a lot listed, but it's similar to Denny's and IHOP so I can find something similar at one of those and use that). It's not perfect, but it's better than not logging at all! And, like I've said earlier, don't eat out so much. When you do, split the portion in half before you start, box the other half up and take it home for a later meal.