Mum,
From what the vet has said,I think surgery is the answer here.We all like to avoid invasive treatment when possible,but this abcess is not going to clear up with antibiotics,and the pus could get into the system and make him very ill.
If you are confident in your vet,and think that he has enough experience of oiperating on gps,then get the surgery done asap.Please do ask your vet how many gps he has actually operated on and what aneasthetic does he use.If you are not happy,look for another vet.You have the right to get the best possible for your piggy.
When you take him in for surgery the vet may advise you to starve the piggy for 8 hours or more.This is not necessary because gps cannot vomit.,and as they are grazers they cannot go without food for that long.If the piggy is going in at 8.30 in the morning,do not remove the food until about 6am.Do not remove the water.
Other members have already advised you to take a companion pig or soft toy for company.,plus favourite food in a tupperware type box.
Make sure you have some vet beds ready for when he comes home,and you will need some 1ml syringes to give him water if he does not start drinking straight away.Have some Critical Care or Recovery handy as well in case he is off his food.,although with this type of external surgery he should be o.k. anyway.