I have a pembroke  corgi bitch that comes into season every 4 months and i have mated her twice with no sucess. Do you think the 4 month cycle has anything to do with it?

As I understand it anything under four months is likely to mean the bitch isn't ovulating.  did you do premate tests to check for ovulation?

Have you used the same dog?  If so it may just be that they aren't compatible.

I am sure i have seen in the book of the bitch, that a dog that has a season every four months can be linked to infertility, i am not totaly sure, check it out.