Bump on inner side of my foot..?

I'm in a musical, I have rehearsal everyday, I've got school, I have chores at home to do, I have robotics, and I'm an all around busy person. Just recently I found a bump (on both feet) on the inside side of my foot near my heel. Maybe it's just from being on my feet all the time but I'm not sure. It's not boney, seems more like a muscle, and it never hurts. Can someone explain what it is please ???