What could cause this? A lot of things, actually. From personal experience, I'll tell you that gastritis will do this, since the walls of the stomach are irritated. Ask your doctor about this possibility. (Have you also been feeling bloated by any chance? What about heartburn? Have you been checked for H. Pylori?) If it is gastritis, then you have to find out WHY it's happening. Again, there could be a lot of reasons.
For the moment, try taking DGL 20 minutes before any meal and see how that helps. (I get mine from iHerb.com, but any of the local health or natural food stores should carry chewable DGL tablets.) You may also want to start taking an herb called shatavari for a little while, which may help gastric emptying time. This'll give the stomach lining a break. Finally, eat smaller, more frequent meals, and foods that are very light on your stomach and easy to digest. (Avoid most meats, anything fried, coffee, caffeine, sodas, Vitamin C pills, beans, any acidic food like tomato or orange juice, and try to keep a low-fat diet for a few weeks.) Potatoes and fish (or white-meat chicken, skinless) with a side of boiled veggies is a very good option.
Your doc may want to put you on something like Zantac or Prilosec just to see if the condition improves, but before going on any medication, talk to your doc. The above recommendations have little to no side effects, though if you're pregnant or lactating, you may want to talk to your doc, period.
@Dizzy247
What you describe sounds like a gallbladder issue. I highly recommend you talk to a doc and see about having an ultrasound to check for stones.
hi, i get sick too after eating. i also have pain in my right hand side, under my ribs, travelling to my back. it goes after i am sick. i had a small headache today too. if you get any answers, i would be interested in what you receive.