Nasal infection, antibiotics help but don't cure

[geexcess]

Max has had a nasal problem for 8 months or so. At its worst he snorts and sniffs and occasionally sneezes blood. We have had xrays at the height of his problems and there is some kind of inflammation in both sides but probably not cancer as there is no bone damage. He has lived in two separate locations and two separate households in the same city, so it probably isn't environmental.

Antibiotics bring down the inflammation and clear his breathing within a few days. 10 days after he stops taking the meds his problems begin to return. We have had him on long courses (last one 6 weeks) of clavamox but the infection comes back in much the same timeframe regardless of the course length.

When sick he still eats, sleeps, poops and plays normally, he just snores and snorts more. We have a good vet but I am stuck for things to ask or suggest and we are just going to put him on another long course - which is better than him having him sneezing blood but it is twice a day trauma and slows him down a lot.

Any ideas as to what it might be or what I might ask the vet to do before we put him back on antibiotics, so they might be more successful.

Thanks in advance,
Gordon