Does not breeding

I wanted to see if anyone else has had problems with does not breeding and if so what could be done to help them.  I had three does from the same pen that didnt conceive last fall and then the fall before that 2 others didnt breed.  I honestly feel like they never came into heat. Could this be their feed? Stress?  Any input is welcomed and appreciated.  Thanks 

Two years ago I did not AI any does from this pen. They were all live covered with a 6 yr old breeder.  He did successfully cover some of the does. However 2 did not conceive. This past fall, I placed CIDRS in all does and gave PMSG at the time of CIDR removal.  One doe (that didnt fawn previous yr) took to AI and the other that didnt fawn from previous season caught back up buck.  The does that fawned 2 yrs ago didnt fawn this yr.  Its as if they re fawning, then missing a season.  What could be missing from their feed that would cause this?  All other pens of does are conceiving and seem to be doing ok.   Its just this one group of does that has had the trouble.   I have since moved them to a bigger pen where browse is better.  Thanks again

I bred with different back up bucks both years and split them last year after the AI and used 2 different back up bucks