I have earlier asked my doctor about stem cell treatment, but my doctor says this is very experimental and lacks a good amount of good research. And since Ankylosing Spondylitis isn't exactly life threatening, it is not worth it.
Currently I take NSAIDs, especially newer medicines like Vimovo https://www.vimovo.com/ helps a lot, but is not something you should take every day. I take it mostly during the long winter months here in Norway, because low temperature makes me really stiff. Chat with your doctor about options here. My mom get tumor necrosis factor-alpha (TNFα) blockers, she says it helps her, but I've said no for now as I don't want to weaken my immune system and I can live with the pain I have now.
Another thing that really helps is regular exercise, you probably already know about it, but you are probably also like me, that just starting with exercise is just difficult. Anyway, you should exercise 3-4 times a week with minimum 30 minutes of sweating. For me it helps a lot when my back is really stiff. And as part of our awesome public health treatment we all get 4 weeks of sick leave annually. Where we travel as group to Turkey / Spain and go through an exercise plan. That is really something that has helped me to still be able to work 100%, You should do something similar even if it cost you money.