Am I not eating right...I always feel sick?

I feel like everyday I'm either constipated or have diarrhea. Also, after I eat my stomach feels uncomfortable, I always have to rub it. I use to exercise alot but ever since college started I really haven't had time. Also, haven't been eating right. For example, today before I went to my part time job I had a grill cheese with mayo, then a Hershey bar, and now for lunch I just ate fried fish. I know none of this is healthy....so basically is this definitely the cause?