lump on face

I have a female guinea pig who suddenly lost weight and has a lump on her cheek but she’s very excited for her meals and eat veggies and hay well and responds to her surrounding as usual .. what could it be? And will it go by its own ?

Hi, I’m new to this forum and joined just to ask about this, I’m worried. This is Gizzy, a few days ago there was an odd spot on his face and I thought he might have scratched himself on accident. There’s no chance he could have been bitten. It’s been getting a little bigger everyday, and now...