When i was a toddler I developed a spot on my lower back in the middle, which grew larger and larger over a few weeks and which then disppeared. It didn't stretch so I couldn't lean forwards and was v painful when I tried to do so.
I remember mum asking the gp about it, he may have given her a cream for it but I'm really not sure.
It's not terribly important, I've never had anything like it since. It's one of those things which pops into my head with a question mark. There' sno one to ask except you lot, parents both dead, brother wouldn't know.