guinea pig sexing

Question
I have 2 guinea pigs,Jamie which I know is a definate female and Janie which I am not sure about.I think that she is female because her genitals are in "Y" shape and no visible scrotum.I recently got the Jamie(1 month old)and when I paired her with Janie(3 months old),she[janie] began to mount Jamie.Should this tell me something? Is this normal?  

Answer
Hi,
 You are right she is a female.If a guinea pig has a Y shape then that tells you that the guinea pig is a girl. Sometimes female guinea pigs don't really know if the other is a male or female. You shouldn't really worry about this because this is normal and soon she will figure out that she is trying to mate a female instead of a male. Thanks for your question and I hope this is helpful.
                                                      Blair