6KG EXAM WEIGHT LOSS???

So I've unintentionally lost about 6kg during exam season.
During this time I've had the most unhealthy, cruddy diet possible.

I'm not even kidding.

I've been living off quorn nuggets, beans and vegan ice cream.

I think it's due to the stress of exams, but all I know is that my leavers ball gown is now slightly too big for me, and that I'm going to regain this as soon as exams are over.

At the start of exams I had a big IBS flare up. If any of you know what I'm talking about you'll understand the pain. It lasted about two weeks before my doctor put me on new meds. During this time was when I noticed it the most, as I was basically living off veg chicken nuggets and crackers.

The problem with this loss is that I'm almost 100% certain that I'm going to regain this weight asap, so it's not worth me buying new clothes and stuff when I'll be 6kg up again within a few weeks.

This yo-yo is extremely unhealthy, and what should be noted is that this weight loss was not in anyway intentional. My diet's at its worst right now, and my main form of exercise right now is walking my dog once a day, as I don't have the time to train.

So basically the point of this post is that I've had a very stressful few months, lost 6kg in 2 months, and will most likely regain this and more.

Does anyone have any tips on how to prevent the regain? I'm not looking forward to looking like my stepmother.....