My guinea had an abscess in his neck - just below the jaw bone. He got it, we think, from eating a sharp piece of straw/hay and once it pierced the inside of his mouth/throat it caused an infection.
I took him to the vet and they knocked him out and lanced it - it cost just over £100. It was a tricky operation because knocking a pig out can be very dangerous in itself because they are so small.
All went well after that first operation but I had to keep the wound open and push any remaining puss out for a good week or so afterwards and to bathe it and administer anti-biotics.
I did this until I noticed a second lump further down underneath his neck so I took him back again. He was, at this point, getting very thin, not eating or drinking and generally becoming very unwell so I asked for him to be put to sleep because it meant having a second operation to lance the second abscess and I didn't want to put him through this and there was no guarantee these abscesses wouldn't come up again.
I was told to give him a few more days 'just to see' if things calmed down - which they didn't so we did have him put down.
To be honest, by this time, I'd spent about £150 in vets bills. I had to draw the line at spending out any more plus, more importantly, I had to think of him and how he felt. OK so it was only a guinea pig but I could tell he'd had enough too.
Please let us all know how you get on with your pig at the vets? Good luck.