When can my rat get pregnant?

  I have 2 female rats and 1 male rat, and was wanting to breed one of my females to my male. Well, yesterday, i put the male and female together, they "did it" a few different times, then i put them back into their separate cages. Just because they did it, does that mean she was in heat? Should i keep putting them together to "do it" in case she wasnt in heat?
If they did it, she wanted it , and she is only ever interested when she is fertile which is a great deal of the time. There is no harm in leaving her with him another day to be sure but you have likely succeeded in breeding her.
You are not a breeder and have no need to be breeding rats. Do you know what two to breed to prevent illness, stillborn or inbreeding? Do you have a home lined up for the babies she will have? Are you prepared to have way too many to handle if you make one sexing mistake?

If you cannot answer these questions then keep them separated and do not breed them, for their own well being.
Well they have to get knock up some how an if that doesn't work give them some beer