My cat who is about 4 years old and spayed has a very swollen nipple. any clue what it is?

It is just one nipple that is swollen and there is a bump extending from the nipple down and kinda out. its very hard to explain. It is missing some hair around it and I'm very worried about what it might be. about a month ago my boyfriend and i found a patch of almost like glued together hair on her underbelly and i'm wondering if that has something to do with it cause now that hair is gone and the big bump and swollen nipple is there. i don't really have the money for a vet right now and wont for maybe a week or two so any help will be greatly appreciated.