Is it possible for my gerbil to get pregnant off one of her children?

[<3Animals<3~4<3Evert~&l]

My gerbils pups are 5 weeks tomorrow. And lately she has been feeling very lumpy like she was when she had her first litter. But her mate passed away. Is it possible for one of her male pups to impregnate her at 5 weeks old? I don't believe it is but she only looked this big when she was pregnant.