The appendix is on the right side of the body, so it can't be that.
Probably it's the spicy foods. Eating too much spicy foods can cause inflammation of the protective lining of the stomach, which can lead to gastritis. In that case, the pain can last for several days. The fastest way to cure gastritis is to do a Water Fast for 3-4 days (= not eating anything at all and just drinking water).