Scary sudden weight gain despite exercise that worked before

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.