For both of ya'lls sake, I'm hoping it's just soreness.
A while back my aunt was having health issues and was in and out of the hospital. We had offered to care for her Oldenburg mare until she was stable. Two weeks after the mare was here we started to notice she was having some hip trouble. After a vet check we determined that it was soreness from the terrain. My aunt lives in FL were hills are almost nonexistent. We, however, live in TN.....in the hills.
So maybe it is just from all the riding...? I wish I had some advice, but really the only thing you can do is wait for the vet.
I hope everything turns out in your favor.
Keep us updated.