It could be food intolerances or allergies. I never put much stock in that sort of thing until I discovered it was what was causing many of my ailments. It's taken awhile to learn which foods cause which symptoms, but it's been worth it not to feel so bad. I had to give up some foods completely because I've developed too severe of an allergic reaction to them. There are other foods I can have on a regular basis in small quantities and others that I can only have once every few days. It hasn't been easy to learn to live with, but the alternative for me is severe joint pain, hives, breathing difficulties and a bunch of digestive problems.