I’ve posted in the past… long time ago and we have been under continuous vet care for more than a year still. Just looking for some input as I’m at a dead end with what else I can do.

Charlie is a little over a year old. We have been dealing with URI for over a year. She has been on antibiotics for most of her life now. Since she was 10 weeks old.  We started with a vet who only kept her on antibiotics for short term and she would be back to sneezing and snot not long after discontinued. A culture was finally performed and she did show a form of pastuerella.. but not the bad one. Appropriate antibiotic was given and again back to sneezing and snot. This vet then said she just had allergies and left it at that. We found a new exotic vet.
Our current exotic vet has been treating Charlie since March 2021. He has done much research and has consulted several times with an exotic specialist at a lab. They decided to treat for pastuerella. Exotic specialist told our vet once we found antibiotic that seemed to be working to keep her on it until symptom free. We have never been totally symptom free. Three weeks is about the average she will remain symptom free.
Charlie has been treated with Baytril since March. Twice we have stopped because of stomach issues to give her a break.

A new culture was done two weeks ago which showed nothing. The lab could get no bacteria to grow. Antibiotics had been stopped before culture. They did get a fungus to grow that is commonly found in hay, but the exotic specialist told our vet that is common to find  and normally causes no problems.
Our vet asked the specialist what to do about the Baytril and she said to stop it. Charlie had just started a new round, and we decided to let her finish it. She has been more sneezy again last few days and still on Baytril. Today she sneezed out a good amount of thick, yellow mucous. Normally if it’s thick, it has been white except for a few times months ago at beginning of using Baytril when we did see some yellow.  Often it’s may just be a watery, clear discharge.
I have done everything I possibly can do environmentally. We have cleaned air ducts. Tried different hays. No perfumes, air fresheners, dryer sheets, etc. We have air cleaners throughout the house and one in her room she sleeps in.
Tomorrow I will call her vet and let him know her discharge is thick again and is yellow.
He suggested last time we talked after culture results 10 days ago the next steps would be a CT scan and possibly endoscopy. He was going to call around and get some prices for me, but I’m already sure even just the CT Scan will be more than I can afford. He said we would be talking thousands.
I know teeth can cause issues, but since this started when she was only 10 weeks old and does ease up and stop at times, I hesitate as whether it is a tooth root issue. 10 weeks seems way to young for such a problem to start.
I’ve had bunnies for many, many years and have never seen anything like this. She has the vets, exotic specialist included, stumped.
I don’t know what else to do for her, especially since the CT scan is probably out of the picture. She feels great otherwise and is happy. She free roams the house and is litterbox trained.
She’s  been on quite a few other antibiotics before we stayed with the Baytril for the last 10 months. The vet says she’s had more antibiotics than probably any other bunny ever.
Any thoughts? Anyone else had this issue long term? Treating for life with antibiotics?