Lame Horse - Suggestions Appreciated

I know my horse is lame but its hard to tell if its just mild soreness from a difficult training session or if its something more serious. I have a VERY hot TB who is 17.1hh. When I say hot I mean like his ancestry War Admiral hot where he needs specially trained handlers despite being a gelding. That aside he had a very serious training session three days ago where he was essentially very, very agressive with the trainer and the trainer just stayed on waiting for him to calm down. He worked himself into circles like a western cow horse for an hour. He finally calmed down but the next day he seemed lame. I put liniment on it and gave it a day's rest. The second day he seemed completely fine and worked as usual. Today he was sore again. My plan now is to give him two days rest and see how he does and call the vet if nothing improves. What exactly may have happened? How do I alleviate the soreness? I'm also concerned because the farrier trimmed him four days ago, could that be it? Thanks

When he walked in circles for an hour, did he walk more in one direction than the other?

My first inclination would be to look at the back. Sounds like it may be sore. I've found this usually the case in lameness that has no obvious source. Try running a hoofpick lightly down his back on either side of his spine and see if one side (or both) appear sensitive. I'd work him lightly for a few days - long low walks and trots, nothing too stressful. Just let him stretch out and relax a little (if he will that is).