Like I said this sounds more like a fungal thing going on here. Getting it looking at by a doctor is the next course of action.
Doesn't seems like an actual blister but its kinda like a pumped vein/nerve...sometimes it seems flat and sometimes its like pumped up....its not at all painful to touch....could it be an STD???
Is there an actual blister there? Is it painful to the touch? Without the mention of the blister this sounds like a fungal infection. I would always recommend getting a check up if something looks out of the ordinary.