@chikkugtavc Did you do a loading phase of creatine?
That can definitely turn your guts a bit.
5g (around a teaspoon) is enough, just builds up over time.
Also whey can effect you if you are a bit lactose intolerant.
I'd carry on doing what you are already doing and removing things from your diet as a process of elimination.
Raw oats might be an issue if you haven't cooked them.
Also, having that all late on (assuming you go to bed not long after) probably won't help.