When is my guinea pig expecting?

Okay so my female guinea pig is pregnant, she is five or six months I'm not exactlly sure because she was given to me, anyways she has lumps in her stomache(I'm guessing those are her babies) and I havnt felt them move but I've seen very little movment . I did not breed her on purpose she was given to me and the previous owner was not a good animal owner. Also she drinks A LOT! I have to refill the bottle every morning and sometimes night , thanks.