Hi,
This is one of my things....we might should move this to the infirmary. Sneezing can be a sign of several different things. Let me comment on your initial post and then offer some suggestions.
It is possible to have allergies. It is also possible to have an infection that causes sneezing without it being where you think it might be. Couple of things for more info...what breed is your bun, age, weight, diet (specific brands of pellets and hay and how much and how often fed)? The comment "limited antibiotics" concerns me. No offense intended to your vet, but that is usually a comment I hear from an inexperienced rabbit vet. And that is not meant to be a flame to the doctor....rabbits present some very difficult challenges. And to make matters worse, the info in reference manuals that many vets still use are woefully out of date....read the inaccurate. I can tell you from personal experience that very little time is spent in vet school on small exotics.
As far as infections, most respiratory infections are caused by a pathogen known as Pasteurella Multocida. It is commonly called "snuffles" which is a term that should be banned by governments all over the world....but that is another story. This bacteria is present in the respiratory systems ofnearly all warm blooded mammals and many birds. Usually the immune system keeps it under control. It can infect any body tissue but is most commonly seen in the upper respiratory. Symptons are somewhat like a cold (for clarity, technically rabbits can't acquire a cold virus...I think it's a rhinovirus if I am correct). Usually the mucus associated with this particular infection is yellowish or greenish in color. Most of the time, the discharge will be present not just when the rabbit sneezes. There is usually a slightly elevated body temperature. Something else to consider in these type situations are dental issues. Molar spurs can also cause a nasal discharge and sneezing but the mucus is usually caused more by irritation more than the direct infection. It is along the same lines of being punched in the nose...your nose or eyes will start to run. Some breeds of rabbits are prone to dental issues. Those that don't eat hay (or eat hay blocks)are also prone to molar issues.
There are some things you can do for allergic type reactions. Many of the exotic vets have devices to look into the nostrils to check for debris. Most often, it is a small piece of hay that is stuck in the nostril. If it is a true allergy, make sure you are using the highest quality pellets and hay. Filter the pellets with a sifter. You can also lightly spritz the hay with water....some people use apple juice or something similar just to give a new flavoring. I do know of some vets that prescribe antihistimines to rabbits. This is quite risky since those drugs tend to "speed them up" a bit and a rabbit's heart doesn't need additional work. There are also some other issues in there too. Some vets use steroids. But while steroids will help the allergy....the suppression of the immune system can cause bacterial infections in other parts of the body. It's risky too. We have had some success with using Children's Neo-Synephrine Nose Drops. And I would bevery cautious when using nasal drugs for humans on your rabbit....remember that any medicaltreatment carriesrisk. Something else that might can lead to a possible cause...and help the condition...is to increase humidity. Contrary to what you would think....cool humidity works best. Cool mist humidifiers are available at very reasonable costs at any pharmacy.
If this rabbit were here, I would absolutely do a nasal culture to see if there is bacteria in there. And there are now many antibiotics we now know are safe if they are used properly. Zithromax is particularly effective against pasteurella (for now anyway). We are starting to see some issues witheven more drugs as the bacteria are becoming more and moreresistant due to improper use....read that as "trying" an antibiotic withour propercultures. Antibiotics are either broad spectrum or targeted. If it is an infection, I would want to know the root cause and the bacteria so it could be properly treated. If it is an allergy, you might have to try different husbandry options to find one that works. And the cool humidity works the best around here.
Hope this helps...and I know that some of my comments may come across as quite "pointed" but no offense or flaming is intended to anyone. Just what I feel are some very important points.
Randy