I have a blister like growth on top pf my foot. It developed 2 years ago while I was wearing a new pair of sandals that kept rubbing that spot on my foot. It is not a skin tag. It looks a lot like a blister but has never gone away, does not hurt. If I try to prick it to drain it there seems to be no fluid in there, just bleeds a bit. Not a blood blister either. Any thoughts on what this could be?