Stress is making me kind of ill

I've only had two exams so far but both times, two days before the exam my stomach turns to mush. I don't know what's wrong with me, I'm never like this.
I've had diahorrea (sorry for being blunt but it happens in life) and my stomach constantly makes bubbling noises. I'm fine the day after the exam though. I'm just worried that in one of my exams I'm going to pull a Will from the inbetweeners. Also a bit gassy too

I'm a very healthy person so I can say with confidence that I don't think it's my diet causing this. I don't feel mentally stressed at all, except from around an hour or two before an exam. Is there anyway of stopping this? I would really like to go out without having the frequent dilemma of trusting the fart or not. Hahaha!

Was... was... was the winking emoji intentional? Bit of a weird usage tbh...

Have you got a decent sleeping schedule, exercising, etc?

I tried to be funny, I'll stop now .
I have a very very very bad sleep schedule, and I exercise when I can; usually in the form of cycling or running.

You should probably try to adapt the sleeping schedule then, (I say this at 3:30am smh) because on some people it can cause havoc. But overall, definitely go to your doctor about this, it seems like you need some help/treatment/diet monitoring.