Hormones are a well known trigger for flares and AS. Many women's first AS symptoms happened during pregnancy and others their AS gets better or worse during pregnancy. Many young people get their first symptoms during puberty. So maybe your rhuemy is "out of touch" with research?
See your Gyno. You might want to get on the pill( or a version) to limit that issue. I was not diagnosed with AS while that age and mild disease would come and go. Mine got much worse during menopause. I was put on a mild version of the pill and WOW oh WOW, I was much better. But, than darn, because I have fibroids all kinds of bleeding issues started. My choice was surgery, which might not be covered because I could stop the hormone pills or just stop the hormone pills. So I stop the hormone treatment. Once I was no longer in perimenopause, my disease did not fluctuate so much---though unfortunately, still severe.
So either get more treatment or see a GYN to limit your hormone fluctuations.