lump on my pacman face

[Dave13]

So my pacman has developed a lump on its face and it has me worried. It's been refusing food for the past two months except for maybe a nightcrawler every 2 weeks or so . last night I got it to eat a pinky rat because it has lost a lot of weight. I found the lump when i was feeding it last night. I've moved it from its cage and into one with damp paper towels and 80 degree hot spot and 80 percent humidity. The cage it was in had an 78 degree Hotspot and 80 percent humidity because she seemed not to like the 80 degree hotspot. The substrate I had it on was about 3 inch coconut soil Changed once a month. Any help before I take her to the vet would be greatly appreciated.