Pain in my stomach and nausea every time I eat--doctors have not found anything w/all the usual tests. Could I have a parasite from travels in india?

Stomach Pain. Not sure if you had all the usual tests. Endoscopy will see into the stomach, and take cultures, and samples of tissue from areas that look damaged or diseased. If this test was negative, and the colon test was negative, and the gall bladder test was negative, you could still have gall bladder dysfunction, or irritable bowel syndrome. Diet changes, medication trial, working on your stress.
Parasites Possible. Make sure that the "usual tests" and workup include consideration of your travel history. People who live there might not show the same effects as travelers to parasites and other pathogens in their water, soil and air. Check with your doctor about getting your stool tested for ova and parasites. Infeccreetious disease specialists might help you and your doctor solve your medical mystery.
Possible. Parasites can cause abdominal pain and nausea but typically you would also have diarrhea, increased gas and foul stool odor. Fever and weight loss are also possible. If you have recently traveled to india, you have an increased risk for a parasite infection. Ask to be tested if you have not been already.