What Should I Do About A Painful, Pea-sized, Nipple-like Sore On The Ball Of My Foot?

I have an odd looking blister or sore of some sort on the ball of my foot it has been there as just a dot but recently protruded from my foot it looks like a nipple about the size of a pea it's very painful but is not a blister because it wont pop if I can send an picture that would be great just so I have an idea of what I should do