What could this possibly be!?

Posted the first picture up a few days ago and now it has blistered and I’m still at a loss for what it could be? Going to the doctors tomorrow, but it’s tripping me out. It started off as little tiny pimples and turned into a blister (despite me not touching or itching it) i had it a few months ago in the same exact spot.. and it hurts to the touch and to bend my arm