Is my pet rat pregnant? how do i know for sure?

my pet rat paula and roxy been acking really weird is it from my male rats scrappy and moe?? i let them have a little play date i went to pet my dog and scrappy was on roxy 2 weeks later now shes been making a nest like crazy eating alot more then usual and has as wider side i read on oline more about this but i just what to make sure and get other pll opoinions thanks i hope u can help