Why does pesto sauce make me sick?

I really enjoy pesto sauce but within 15 minutes of eating I begin to have a serious stomach ache as if I were punched...this goes on for several hours. Then, once my stomach quits hurting I get intestinal cramps that are out of this world. Periodically for the next 6+ hours I confine myself to a bathroom. I have no problems with any pesto ingred. such as cheese, olive oil, and garlic...except sometimes basil. Once in a while cheap spaghetti sauce will get me in a knot. I always thought basil was good for digestion and good for calming ailments. Does anyone have any clues why I would experience such things?