Possibly Guinea Pregnant?

Question
Just curious My guinea Pig has Gained weigh latly. and Shes fat from waist down and Notice To Big Nipples. I held her over a bit to check.
Im not to sure how to check for babies. But I really think she may be pregnant.  she wasnt this fat when I got her...  
How do you tell if shes Pregnant  And Nipples wise..
they are Kinda long and Sorta Dark

Answer
The first question of course is "was she with a male?"  You didn't say how long you've had her.  If she's relatively new to your household she may have been in a pen with males and was pregnant when you got her.  

You cannot always tell my looking at the nipples.  If she's had a litter before, her nipples would be longer than a pig that has not had a litter.  The gestation period is approximately 70 days.  You will feel movement about two weeks before delivery.  

Looking at her size and weight isn't always an indicator of how many babies she might have.  Some sows get very large and others don't.  But a sudden and steady increase in weight does indeed sound like it could be that babies are on the way.