I've had a bit of background story from Ellie...the piggy in question is 4-5 years old with a lump on her chin which seems to be affecting her ability to eat (dropping food etc.) the vet says that piggy is too old for an anaesthetic and that an FNA (fine needle aspirate - to extract some contents of the lump to see what it is) is too dangerous.
My questions to snaps.aisha...
1) where exactly is the lump on your piggy's chin? This lump could be a number of things, but being on its chin its obviously affecting her ability to eat, likely causing her pain. Have you ever had toothache? If not, you're lucky, it's very very painful!
2) do you know what the medicine was that she was given? If you don't know what it was called, do you know what type of medicine it was or even what it looked/smelt like? What did it do that made her sick?
3) where abouts in the country are you? It sounds like your vet isn't very experienced with treating guinea pigs. Vets aren't taught very much about exotic animals while training, they study them for pretty much one day a year. Guinea pigs are classed as exotic animals, where as vet training focuses more on dogs/cats/horses/farm animals, and guinea pigs are quite different to these. If you let us know where abouts you are, I'm sure that someone would be able to recommend a very good vet who is experienced with guinea pigs. Your guinea pigs age shouldn't be an issue for investigating this lump, and get the right treatment.
You mentioned your mum spoke to the vet...are you under 18? If so going to the vet is the responsibility of your parent(s). Could you show them this thread so that we can help them, you and piggy find a knowledgable vet? Going to a vet who isn't experienced is often just a waste of money as piggy isn't getting the treatment to get better.
In the meantime, its important to keep getting food into her. Keep getting the liquid food in, and if she eats guinea pig nuggets, you can try softening them with hot water, she may find it less painful to eat them that way. You'll know how much guinea pigs poo, its really important to keep an eye on what she's pooing as this is a sign that she's getting enough food. If they become small, increase the food, if they stop, she needs to go to a vet ASAP.
Hopefully we can get this sorted quickly for her and you
