I have this kind of lump on the inside of my elbow under my bicep. I'm only 13 and I don't know what it is, I don't know if its a growing pain but its been there for a while. If I fully extend my arm with my palm facing up and I move my finger around there will be a lump. But if I close my arm it will not be there. If anyone has expirenced this please let me know or help me figure out what this is.