It could be gastritis (inflammation of the stomach lining). I have chronic gastritis and when it flares up, I get nauseous every time I eat. Basically the lining is inflamed, so when the stomach produces acid to break down food, it's like pouring acid onto an open wound- that's how my doctor described it to me. Mine is caused by B12 and iron deficiency, and possibly an autoimmune disorder. There's a lot of possible causes of gastritis, and a lot of possible reasons to feel the way that you do, so it's definitely worth looking into more, but that's my initial thought

Could be diverticulitis..... go see a doctor