Hi
I have AS for about 8 or 9 years, and it was only on the past 6 months that the pain spread to other parts of my body. My shoulder, a foot and a knee were "attacked" in this order, month after month.
Pain in the hip is very common for me. I used to suffer a lot from sciatica, that caused me lots of pain from the hip down to the knee. Maybe you are having a flare of sciatica?
Hope you get better
Zélia