how to tell if a guinea pig is pregnant

Question
I got my guinea pig 1 week and 4 days ago and I put her in with a male. she is getting slightly bigger in the back and sides. i think she might be pregnant because when i got my first guinea pig (boy) and the other one tried to mate with it for 3 weeks but with my female he stopped in 1 day. i really need to know if she's pregnant so i can treat her properly. please help!

Answer
Kenzie,

It is difficult to tell for sure, as the female comes into season approximately every 16 days for a period of about 12 hours. So most breeders leave the male and female together for five weeks to 6 weeks. Once pregnant (or "in-pig" as it is referred to), the female will try to fight off any further amorous attention from the male.

Other signs include,

Drinking lots of water,
Eating more,
Becoming noticeably heavier,
Teats become more prominent and red looking,
By the round belly she'll get further along.

I hope this helps,
 Take care,
   Jules