Hog Island Boa has mouth "tumor" and RI - Desperate for Answers

[Aleta Kane]

About 5 weeks ago I noticed that my previously perfectly healthy, adopted Hog Island Boa, had a significant amount of bubbles coming from his mouth. I took him right to a vet and started him on the antibiotic Ceftazidime. The vet reviewed his environmental conditions and said they are perfect for him; temps 85-90 degrees, humidity 60%, heat lamp 18 inches, under belly heat, healthy sheds etc. The antibiotic did nothing for him and after about two weeks he developed what looked like mouth rot, this went away after a few days.
The infection continued and the” mouth rot” came back even worse. The vet then put him on Baytril administered by me every 48 hours, it still got worse. I took him to another more experienced vet to get an opinion. The vet thinks that it could be a tumor not mouth rot and wants to do surgery to remove it. He said it is too hard to be mouth rot. The vet is unsure of the type of tumor until a biopsy can be done.
I do not understand how a tumor could have developed in his mouth in a few weeks and previously come and gone. I am very leery to do surgery because this far nothing the vets have done have helped; only made things worse.
Has anyone ever seen or heard of anything like this? Could it be a reaction to the antibiotics? Has anyone had a snake undergo surgery like this?
I am beside myself and desperate for answers. Thank you for any information you can give. Photos below show outside of mouth but not inside.