Recently I Seem To Have Developed Stomach Issues. It Comes

Recently I seem to have developed stomach issues. It comes on at the most obscure times, in the middle of the night, after eating just about any food and with pretty much any liquid. My stomach feels as if it is on fire and is going to explode. Sometimes I vomit, I get feverish, chills and am very lethargic lately. I always feel as if I am going to vomit. Is this an ulcer or form of? I don't have a lot of money to spend on doctors right now so I am looking for a OTC remedy to hold me over until I can get to the doctor.