Bump on the top of my head?

Hi, I've seen many questions on here that are similar to mine, but none exactly. So I feel I should ask my own. Anyway, I've had this ump on the very top left side of my head, towards the back. I noticed it about 8-10 months ago. It was pretty random, I was aying there and slid my head backand felt it. For a few weeks I lost hair in the vicinity of the lump. Then the hair grew back and the ump went down. It's always been there, but for the most part it didn't really bother me, just annoying. Well recently it decided to swell back up and has been tender to the touch. It went back down to the size of a pea but feels very sore when I put a hat on or rub t. I'm quite worried about this little booger now. I've made a doctors appointment for Monday but i'd like to ask you all for any nfo on this for some peace of mind. Any answers are greatly info on this for some peace of mind. Any answers are greatly appreciated. Thanks in advance.