I guess my triggers are similar to most of the others on this post: lack of sleep, low pressure fronts, etc... Except I've also found that traveling (e.g., flying) is one of the worst triggers for me. I can take a simple 1.5-2hour flight and I'm in agony for at least the first few days of my vacations! Now I just make sure that my vacation spot has a pool, as water therapy works well for me.
I have had hip pain from the very beginning (more than 10 years ago). My rheumatologist also told me that if I had hip pain, it would be in the groin area. Most of my pain is on the sides--cannot lay comfortably on my right side anymore, and only occassionally does it transfer to the groin area. Sometimes I also feel it in the buttock area, which doctor confirms is legitimate hip pain. But I mostly feel it on my sides.
With a major flare, most of my joints are affected (neck, shoulders, elbows, wrists, hands, hips, knees, ankles, and feet--did I mention my jaw joints too?). With a minor flare, my knees don't typicall bother me that much, so I know when they start aching that a major flare is coming on.