it could be a bruise, i could be something pulled, it could be a tumor, it could be a baby, it could be all your repressed feeliings tied up into a knot on the side of your lower abdomen. you better ask a doctor. no telling what they'll do. probably touch it and ask you questions and try to figure something out based on the information you give them and what they feel and all the stuff they were taught in medical school and everything.
GOOD NEWS!: appointment schedulers are standiing by.
Go to a doctor and tell him/her about it. This is a physical irregularity, hence no one over the internet is in a position to tell you what's wrong or advise you. Doctors can't do anything to you without your permission, in case you're worried that you have an ovarian cyst and require surgery.