Lump in cats skin?

I have a 9 year old cat who I love and adore deeply, I've had her since she was a 7 week old kitten. About 3 weeks ago I noticed a tiny lump on the back of neck under her head. It just so happened that the night I noticed it, was my last night I'd be home for a couple weeks because I had to go out of town for work. I left her with my family and figured by the time I'd get back, if the lump was still there I'd take her to the vet. Well I got back home a couple days ago and she still has the lump and it's actually gotten bigger. It feels to be the size of a small blueberry but not as thick if that makes sense. She's been acting normal for the most part just has been more vocal than usual but I figured it's because I was away from home. She has an appointment next week to have it checked out and I'm honestly so scared, I don't want to hear news that she may have something serious but I also know that it's crucial to figure out what it is. Has anyone had experiences like this where you have found a lump on your cat and what did it turn out to be?