Cat with sore on lip (pic included)

My foster cat gives me more worries!!!!!!!

I made this thread yesterday about her...

http://www.thecatsite.com/t/245496/nursing-foster-cat-with-constant-diarrhea

And now today I'm worried about this lump on her lower lip! After she had her spay I noticed it and was just thinking it was a weird thing that would go away but it keeps getting bigger and now today it looks like this...



Anyone ever seen anything like this???

I swear, she can never just be healthy!

My friends cat had a sore similar to that on her top lips. The vet said it was a rodent ulcer. She has to take some medication and have an injection I believe.
 

Our female (Chai) was a rescue and she had a similar sore on her lips. The vet had a look at her and found some ulcers in her mouth and she was quite lethargic. It turned out to be calicivirus. Hope she's ok and it's nothing serious.

Hi there, we have just adopted this ery same breed of cat, male about 1 yr old.  He has the same sore on bottom of his lip.  Only bigger.  What did you find out it is? I am not paying hundreds of dollars on tests. Our vet likes to dig into our wallets as much as they can. I want to go in educated with an idea of what it is...

Thanks for your help!

Michelle