How long could a dog have an abscess before it erupts? TWO months?

The vet def should have know what it was the first time around. If she/he actually looked at the substance under the microscope- they would have know it wasn't a tumor but rather a cyst or abscess. Is your dog still on antibiotics? if not- should still be on some if the swelling is not done. Also- did you clean the area very well before and after you drained it because it is important to keep the area very clean and clear of any more bacteria. Is there a big hole? I def. recommend finding a new vet! Good luck to your pup!