As the others said, male dogs do not go into heat. I take it he is probably not neutered? This is very normal behavior for a dog, even females will do it. Good chance it is due to hormones. If he is not neutered, I would strongly recommend you do so and this behavior *may* subside. It would be better for his health also.
As for the crink in his back (and I'm pretty sure I know what you are describing) this is just from him being aroused and goes away as his excitement level subsides. Nothing to worry about.