Pregnant rat?

Question
I think my rat is pregnant. I can see her nipples a little bit when she stands up on the bars of her cage, just little dots, but its definitely noticeable, and shes been acting a bit different. Not aggressive, but more calm and shy, and pretty jumpy. Shes been hiding things in her bed, like paper and fabric, but all the shavings she shoved to the other side of the cage. Now theres like a 2 or 3 inch pile on one half, and nothing on the other. Just this morning i realized she was getting bigger(im pretty sure) in the middle. I heard they don't show until a couple days before, how close could she be? I also heard about the heat thing, but when I touch her behind she doesn't do anything different. I was checking every day for like a week, and she hasn't done it. Is that a sign she could be?
Shes been with the male lots since we got him(always supervised), like 2 months ago, and I have seen them 'doing the deed' but shes shown no signs of being pregnant till now.
If its likely shes pregnant and close, what should I do to prepare for the pups? Whats the best bedding to give her to make a nest? Should we stop taking her out of her cage until she gives birth?

Answer
Chances are she is Pregnant, Anytime two rats of the opposite sex and are not castrated and are together there is a definite possibility there will be mating and pregnancy. She is getting close I would not take her out of the cage as much but letting her stay inside and just pet her.

Good luck