Horse riding heavy on the bit. Advice?

This is gonna sound meen, but trust me my pony was the same way and this worked. Use the Kimberwick, and when he tries to plow his head down. Halt ASAP. Jerk his head up and back him up five steps. Then relax the pressure and try again. Be patiant. This is a long time habit that is gonna take a while to fix. And for stopping, if you are inside, turn his head into the wall. Let him hit his head. It wont hurt nearly as much as you think (that's what my trainer says anyway), and after that first time, he probably will learn his lesson. Don't blame him or yourself. He will learn with time and patiance.