are your does over weight?
They are of correct age for their age to be bred, so that would be one of the first things I would check. The way to do that, would be to run your hand gently over the rabbits back. If it feels sharp, then the doe is over weight- and if you have to press down to even feel the spine, they will be over weight. I would also check your buck too, just to be sure he isn't the problem.
Hay is a good thing to feed over weight rabbits, as it isn't the type of thing that would make them gain more weight, yet has all the fiber that they need. It is also good for their teeth