Doesn’t sound like appendix, you don’t say whether it is at the front of your leg or the back. This makes a big difference! Your appendix is in your abdomen, on the right hand side, not near the top of your leg. This could be a muscle strain or a trapped or irritated nerve, but it is not possible to tell without more information – and that kind of information ought really to be taken to a health professional. If you are really worried, go to the Doctor anyway, it is not wise to take risks with your health!