And make sure you male is working. The first time I tryed mice I went for the "cute" colored male mouse instead of the albino that I saw breeding while I was at the petstore and I lost a months worth of production because of it. Fed him off, went to the petstore and watched the mice for about an hour until I saw a male breed with a female, bought him, and now I have alot of offspring and pregnant mice from him I also got a interesting female that did not get pregnant for two months, I saw going to feed her off but dicided to wait and just the other day I noticed that she was pregnant. I guess she waited until she was big enough.