Hi, I Am Very Urgent, So Please Help Me. I

Hi, i am very urgent, so please help me. I have something on my foot that looks like a blister but it is inside my foot and hurts when i walk. It is also yellow/white in the middle, and red/purple on the outside. it is round and i cannot pop it because it is in the inside of my foot and has been slowly growing since last week. what should I do and what is it?