I've been doing dressage for about a year, both my horse and I were progressing nicely, but then something changed. I'm not sure if it was because I was asking too much of him, but he started to tense up his right side. We do shoulder in, leg yields, shoulder out, shallow loops, and lengthening in our warm up, so nothing too advanced. We have huge problems when on the left rein - he cannot do a shoulder in, or a leg yield on that side, and he also has a difficult time bending that direction, as it requires his right side to stretch more than he's comfortable with. He isn't being disobedient, I can feel that he is trying, his mind knows what I'm asking, but his body just cannot preform. The canter is also a problem, on the left lead he is OK, but on the right he is very unbalanced. He tries to put more weight on his outside hind, while still trying to maintain a right lead. He is also unable to move over his hind end, he's sort of 'clenching' if that makes sense, so he sort of 'hops' behind. Transitions are similarly difficulty, he just cannot slow down once he gets moving.
Anyway, how exactly should I go about dealing with these problems? I feel at fault for a lot of this, I'm the one asking for these movements after all. The massage therapist is out every 6 weeks, he gets medicine from the vet to help with his joints ( no idea what the medical term is) every 6 weeks as well, both of which help. Are there any exercises that will help loosen him up, without causing more tension in his body? If these problems are ' part of him' how should I go about riding, should I change disciplines ( he was a jumper before I bought him) or should I just keep going at our current level?