Yes, you'll definitely need a bigger cage. You'll at least need a second cage to seperate the male pups at 3-4 weeks. Otherwise, they can get any and all of the females (including the mother) pregnant!
Make sure your ready for the pups, if you plan on keeping them. You'll need LOTS of cage space. If your mom allows the extra vet bills, food costs, cage cleaning, and cage space, then go ahead and keep them. If you think your parents won't allow all this extra cost, then you will need to get rid of most to all of them.
JUST for the girl you have now, you'll need a minimum of a 2x3, preferred 2x4 cage. But, since she's having babies, you'll need more space.
For her and her babies, you'll need a 2x4 or a 2x5. By the time 3 to 4 weeks rolls around, you'll need another 2x4 or 2x5.
As for right now, I would house her in a 2x5, or at least a 2x4 to house her babies and herself for the first few weeks. Then, begin making the second cage as soon as the babies are born (because you won't have long until it's time to separate!).
When the babies are born refer to this site for correct cage sizes. (broken link removed)
Also, refer here.
https://www.guineapigcages.com
Be prepared to provide a total of 2x6 or 2x7, divided of course for male and female.
Also, be prepared to neuter the boy if he's the only one, get him a friend, or give him away. Pigs do better when paired with another pig.
You'll also need to know about cage proofing for baby pigs, pregnancy, diet for baby pigs, ect.