Possibly have the vet out. I had a quarter horse who was not noticeably lame, but over time we noticed one side of his hindquarters was 'taller' than the other (looking straight at his butt one side was noticeably uneven)
Had the vet out and turned out he pulled a muscle (it was on in his hip area) from being cast in a stall and was lame and had to be put on stall rest for a little bit.
Good luck with your pony!
Take a ride across the badlands
Feel that freedom on your face - Breathe in all that open space
You'll understand why God made -Those fly over states