What's this thing under my foot?

I have a blister like thing under my foot and I was wondering if I should get it checked out. I've cut it open before and some white stuff came out so I thought it was just a blister but I've had it for some months now. Picture: https://imgur.com/a/N5Fkb
Asked Mar 14, 2016

TIP: If it's not your answer to this question, please click "Leave a Comment" button under the question to communicate with the question owner.