is my guinea pig having babies

Question
i have a female guinea pig and am not sure if she is having babies or not she has a round belly and is getting a bit plump she first done it on the 28 july and it was her 1st time so how will i no is she is having babies or not how long they are carrying them for and when would she roughly have them  thanks regardslaura "

Answer
Has she been with a male? What do you mean she first did this on the 28th? She had a litter then?

How old is she?

Please read in the meantime:
http://www.guinealynx.info/reproduction.html
http://www.cavyspirit.com/breeding.htm
http://www.guinealynx.info/breeding.html