You are under a lot of pressure and stress, and have a ton on your plate (figuratively speaking!). I know and understand it well - I am working on my dissertation too, and have a full-time job, and am going through IVF... the time crunch and emotional/psychological stress of trying to get it all done and not let any of the balls drop just gets overwhelming at times.
A few suggestions, in case any of them are helpful for you:
"Don't let perfect be the enemy of good," especially with regards to the eating. Make the better choices where you can, and forgive yourself when you slip up - don't let it turn into a slide, just make the better choice the next time around.
Get some sugar-free gum or sugar-free hard candy to keep your mouth busy while you're studying and have the tendency to eat mindlessly. I love the sugar-free cinnamon candies from CVS; at 9 cals each, I'm not going to do a ton of damage even if I manage to consume half the bag.
Do you enjoy cooking? When you need a break from the writing or feel like you're just spinning your wheels, spend an hour cooking up multiple portions of healthy things you can eat when you need some real, satisfying food. I like to grill or broil turkey sausages and a whole bunch of vegetables - zucchini, red bell peppers, mushrooms, eggplant, asparagus, onions, tomatoes, etc. I make a bunch and portion it out into containers, and when I need something satisfying I have a filling, high-protein 300 calorie meal waiting.
When you're craving carbs, eat something that's stick-to-your-ribs with some nutritional value like oatmeal or half a sweet potato. The low-sugar instant oatmeal packets are just ~130 calories, and a sweet potato can be cooked in the microwave in just a few minutes.
EXERCISE. Seriously. Plan and take 30 or 45 minutes and go for a brisk walk, or take 15 minute breaks here and there and do some squats, lunges, pushups, whatever. The added calorie burn from the exercise is a secondary benefit; the real benefit of the exercise will be the reduction in stress. Focus on the exercise when you're doing it, however short the period might be; the complete mental break from thinking about everything else that is going on will be very beneficial, and the endorphins from the exercise will re-energize you. I used to think people who said exercise was energizing were bat-sh*t crazy, but I swear, exercise was what kept me sane when I was studying for my prelims.
GOOD LUCK with the writing and wedding planning; it WILL all get done eventually, and this period of stress will pass.
