On June 1st, I got a male and female gerbil. Their cage was small, so we upgraded it 2 weeks ago. The female has gotten strangely big, and my family doesn't think it's just the fluff of her anymore. When she goes to sleep, it seems like something is keeping her from falling asleep. She is very active when shes awake. Her stomach is sorta lumpy. It feels a little hardish, like a gerbil could be in there?!?! I did get them to breed, and they are from the same litter. The pet store lady said any gerbils can breed if its from the same litter, to the child and mother/father.
Before I go, I am gonna tell you something a little silly:] - When we got them, there were 2 litters in the cage. Here's why-the main litter was from the Father and Mother; but then one of the baby sons got the Mother pregnant again! Silly Gerbils !!!!!: D
She probably is pregnant, rodents are prolific breeders. And if she is you need to separate the male from her before she gives birth or he will eat her babies. It sounds brutal but its true. Good luck!