Your horse could possibly be becoming ring sour. He could be feeling overwhelmed with the new work load he has. As other have suggested try a trail ride, definitely try get out of the arena! Give him some time off as well. Maybe for 3 or 4 days just bring him in to groom and give him some love so he knows that going in the barn doesn’t always mean work. Also just lead him around the arena a few times and walk out. That will show him again that arena and barn doesn’t always mean work. After that couple days off I would decrease the amount of time you ride to a half hour rather than an hour. Continuing to do this sort of routine a while may help him until he is ready for normal work. Rather than surprise him with regular work again this will ease him back into it. Sometimes we have to take a few steps back so we can move forward again. All the other things people have suggested could very well be a possibility as well. Do whatever you think is best for your horse!