I don't know if they'll show or not, but I'm so scared it's something serious! My family can't afford much, and we want to avoid surgery.. My mom thinks we'd have to put her down, but I really don't want to do that, seeing as she's only a few months old.
Does anyone know what it could be? I have a vet appointment on Thursday, but I'm really curious and scared.
- You can quote me
It's possible it's a harmless fatty lipoma: those often form in the dewlap, but usually on older pigs.
Please make sure the vet you take her to is cavy-knowledgeable. Most neighborhood dog/cat vets aren't. Guinea pigs, rabbits, and other small mammals are known as 'exotics' in vetspeak, and their care requires specialized training and knowledge that the vast majority of 'normal' vets don't have.
Please keep us posted on how she's doing.
Having said that, this sounds reminiscent of Roxy with her abscess. Is the lump movable? Does it feel like it is under the skin? Is she painful when it is manipulated? Does it feel hard and spherical? Or squishy?
Tooth involvement would be consistent with eating less and thus with change in poop output and consistency - though you note that she doesn't seem to be losing weight.
Weigh daily! That's really important.
Others who have more experience can weigh in on whether a tooth abscess sounds possible (or whether my thoughts are coloured by my recent experience). I'd say she really needs to see a vet asap, so it's good that you have an appointment for her. They may well want to do some imaging of the area.
Keep us posted on what the vet says. Wishing you both the best.