Is my rat pregnant?

Question
I just got a male rat and I think my female may be pregnant. But I want to know for sure. It's been 23 days and she hasn't had babies yet or even made a nest but she is huge and her nipples are enlarged. She has also gotten a little agressive to her cage mates and she attempted to bite me. The only thing I'm concerned about is that she hasn't had babies yet.

Answer
 It sounds like she probably is pregnant.  Without knowing the day that she mated exactly it is impossible to tell when her due date is.  Sometimes rats go longer than 23 days.  Keep an eye on her for any sign of listlessness or distress as this can indicate a pregnancy complication.  You need to remove the male immediately or he will breed with her again right after the babies are born and this can be very hard on her body as well as both litters of babies.