It most likely is a worm. Probably a roundworm like the other guy suggested. You could see a doc but the meds they give you isnt good for your body. Id suggest natural remidies, like eating pineapple, raw garlic, shredded coconut meat, or drink few tablespoons of apple cider vinegar or coconut oil daily.
Almost everyone has worms/parasites, they're as common as bacteria. I don't recommend you trying to kill em with harmful treatments or anything because they are made to survive, so they could scatter to other parts of your body such as sinus, eyes, ears, brain and other organs to try and get away from whats killing them. Just look through the forums on this website, there is a lot of info and help here