abscess on chest

Your best bet is to find a cavy savvy vet and take your pig in to get it checked out.

Ditto to what Ly said.

When my GP had an abscess it was there for a few days, until I realized none of the other pigs had the same bump, LOL, such ignorance. Rushed him to the vet the following day. All he did was pop a needle into it and drain all the sludge in it. Home treatment consisted of washing out with a syringe and saline solution and neosporin. It filled back up again, but drained itself the following day. Scabbed over and went away.

But do definitely take him to the vet. It may be something else, and even if it is an abscess, sometimes letting them burst on their own can be fatal depending on where and how it's burst.