that is so hard, and I certainly relate. Spondyloarthritis flares can be brutal in their length and severity! To answer your question, the longest flare I ever had off biologics was about...6 months. When I am off my biologic I am in almost a perpetual, never-ending flare. When I am on my biologic, they are much more short-lived and a lot less severe. I would say my longest flare on biologics was about a month or so.
Biologics do help me flare less often, too. For me, they sort of take AS down from a screaming fiery roar to a dull ache. I have gone through a lot of ups and downs on biologics though, from near remission to losing remission to trying new biologics that I didn't respond to, to finally landing on one that helps just enough. It's a process.
Since you are undiagnosed, is your general doctor prescribing the prednisone? Perhaps you can ask for some pain medication to get you through to your appointment given that prednisone hasn't helped enough. When you see the rheumatologist, some things to ask for would be imaging (X-ray or MRI of your most painful spots) and an HLA-B27 genetic test, which can cinch the diagnosis of AS if you are positive. If you are negative, you may have another form of spondyloarthropathy, which can be just as painful. Here's some more info that may be helpful if you haven't seen it already: https://ankylosingspondylitis.net/diagnosis/
Please do come back and update us and let us know we can help in any other way! -Diana (Team Member)