Do my Gerbils have allergies?

My gerbils have bloody nose and I heard that that can mean that they have allergies to something, I have aspen bedding, and I feed them the same food that they ate at the pet store, my dad thinks they might have been just scratching at it, or they have a cold because they where outside (in my car) for a while, because I could only find female gerbils at a pet store pretty far from my house (all the pet stores around my house only had males) but I'm just not sure what to do, could anyone help!!! ^^