pregnant or not ?

Question
we purchased two guinea pigs for christmas and now one is growing bigger than the other.  We took them back to the store one month ago and they assured us that they were both females...
now they are fighting and the bigger one is having problems walking and has a larger hind section.  What should I do?

Answer
Ok, the problem with "pet store piggies" is that males & females are housed together... She may be pregnant from before,...have you noticed that the "babies" are kicking? Pet stores USUALLY do not know how to sex them! I would reccomend taking them to the vet to see the sex, and have the vet check up on the one  that is having problems walking!

Good luck
Jess