100 Breast help.

I used to have a short, choppy breaststroke. I could go fast, but it really took a toll on my endurance. I'm trying out a new form where i'm supposed to "glide" longer, yet be able to move faster. My coach said my problem is that my head movement is too much "up and down" and then i need to work on getting it accelerated forward. Can anyone tell me what I need to do to achieve this? What drills I need to do?

Thanks