Is my guinea pig pregnet???

Question
Hi,my name is Krista and my friend has a guinea pig staying at my place and we thing she just might be pregnet.We really don't know if she was bred or if she was bred when it was,but we do know that when the past owner got her he kept both the boy and her in the same cage for 2 weeks and when I got them I had to keep them in the same cage for 2 days while I got 2 cages ready for them.We don't know if she was in heat but the past owners sister said they,well,you know for awhile seeing how they were in the same cage,but they don't know if she was in heat.But we looked up the signs of being pregnant and she is getting a little heavier in her hind quarters and looking a little bit pear-shaped and she has been eating a little more then usually and the other guinea pig,but we cant feel anything when we feel her belly.I also have a few questions:
1:Will her nipples get bigger if shes pregnant?
2:Will she run around her cage more when you come into the room where she is?
and 3:If she isn't pregnant how do you tell if shes in heat incase we want to breed her later in the future?

Answer
Krista,

1. Yes, her nipples will get bigger if she is pregnant.
2. No, she won't run around her cage more. She'll start to get slower and not move a lot as she is becoming heavier. As she gets closer to her due date she'll hardly move at all.
3. Sows come into season approximately every 16 days for a period of about 12 hours, so leaving a pair together for about five weeks should allow plenty of time for mating to take place. Once pregnant (or "in-pig" as it is referred to), the sow will try to fight off any further amorous attention from the male. At this point she should be moved to her own cage to go through the pregnancy and give birth.

But from all the info giving I would say she is pregnant and since you don't know if she has been breed before or not I would recommend taking her to see a vet especially if she is over 8 months of age as if so she may need vet help when she starts to give birth.

I hope this helps,
  Take Care,
     Jules