Horse resisting leg aids?

My 5 year old gelding is resisting my leg aid. Whenever I apply the aids he puts his ears back, head up and stiffens his body in the trot and he begins to resist going forward. Whenever I ask for the canter aid he often kicks out (this did develop into a serious bucking issue which I used the "circle" method to stop him from bucking) and now he will often just kick out and rarely a buck. Sometimes he doesn't kick but he is still resisting the aid and often he will fall into the canter and rush. Another issue is sometimes he will just ignore my leg (especially on the right rein) and not listen at all (but this will eventually develop again into him misbehaving). I would like some suggestions on what I can do to help him accept my leg.. he is an extremely sensitive horse and I am hardly using my leg at all, it is a very light squeeze and I mostly ride him from my seat. When I was on the ground I found another thing that was unusual.. when I put pressure in the spot where my leg would be he would put his ears back and turn his head to me (but I am certain he is not sore in any way, we have had the vet check this).. What could be the problem and what can I do to fix the situation?