Birthmarks

My 11 week old was born with a birthmark on his knee, about the size of an olive. It's bright red and raised, a bit like a blister. I know they will go away or fade as he gets older, but I have noticed it has gotten bigger over the last couple of weeks. Also, a tiny dark spot has appeared at the top of it, looks like a mole. I have a doctors appointment in 2 weeks to check it out as I'm worried about the spot and growth of the birthmark. Does anyone else's Bub have a similar birthmark?