Abscess returning even after it has been drained?

Hi! Just looking for any advice really, my dog is 3 years old and a Golden Retriever/Labrador mix, healthy weight and hasn't been neutered. A few weeks ago, he got an abscess after injuring his shoulder internally. We had to get it drained and he was on antibiotics for 2 weeks, he's been off them for nearly a week but the abscess keeps growing in size, I can tell it's starting to bother him since he isn't shaking himself as hard and seems to be less energetic. Notes to be said, the vet did not close the cut she made for the drainage. She said he had blood clots that needed to be expelled naturally since she could not get all of them. His wound does not look infected and it's starting to close up, it's also not bleeding anymore but the abscess won't stop growing and it's getting very worrying. We sent pictures to the vet in an email after she asked but she hasn't given us any news and since then it's gotten bigger again. Did she mess up or is it just normal for such things to happen? Or is it just a natural thing for abscesses to come back?

Hello - I'm a little concerned that the only possibilities given here were that the vet had messed it up, or it's natural for an abscess to return (and it will always do so).   In reality, life is much more complicated than that.  It's normal not to close holes where there may be infection or an inflammatory reaction present; any suture would act to exacerbate it, and holes can be best left to drain so that the purulence doesn't build up beneath the surface.

That said, there must be a reason that the abscess has returned.  Sometimes, for example, there is a foreign body deep down in the tissue somewhere that needs to disintigrate or resurface.  Sometimes there may be cancer involved.  Antibiotics are only going to be effective if a) an infection is present and b) the bacteria in the lesion are sensitive to that antibiotic.  So, not every case will respond to that treatment.  It's a good idea to go back to your vet and explain and come up with a plan to investigate further and / or to treat the lesion.  As a vet, I always found my pathology lab microbiologists or histologists to be a very useful people to call when deciding how to treat such lesions.  Wishing your little one more comfort soon.