I have two Guinea pigs both girls , one i had since it was 10 weks old but the other one i just got about 5 weeks ago there the same age the one i just got had babies at the petstore. they got along fine but one of them made this humming sound and was shaking her but in the air back and forth and trying to get close to the other one. but she wouldnt let her. could one be a boy? i tired to see but nothing came out what should i do?

Optional Information:
Age: <1; Female; Breed: Guinea pig

Already Tried:
my vet