What should i do for my thoroughbred's feet/legs?

I got him about two months ago and he was perfectly fine. We put him in the pasture and his shoes fell off soon after. About a week later he started looking funny on his front feet, like it was hurting to walk even two steps. I took him to the vet to get him checked for lameness, tenderness, etc. The vet checked all four legs and feet and found nothing other than the two front feet were extremly sore. I was told to put new shoes along with pads on him to help. This helped with the front feet, but now his back legs seem to be hurting him. It looks like hes just dragging the back left. Any ideas on what to do with him or anything to help him?