My Hips Drop in Breaststroke

Hello,

So my coach says my body isn't in streamline because my hips are dropped in breaststroke. He says that after I kick I am supposed to pull my hips up but I try that and I am still not doing it right. He says I am going up out of the water, but my hips don't rise after I press down so I don't create that dolphin-like wave. My abs and are very weak and my stroke is predominantly from my kick. My flutter and fly kick are also terrible and my feet are very inflexible. How do I fix this? Thanks.