What Causes Sore Mole On Thigh?

I have a mole on my thigh and it is very sore. I have had this mole on my thigh for years but this is the first time that it actually hurts. I had to put a bandaid on it so it wont rub against my other thigh. I have been walking a lot lately just for exercise and very far distances do you think it could be irritated from that? HELP