Are you breastfeeding? If so, it is very unlikely that it is allergies. If not, you may want to try a different formula. Also try changing the detergent you wash your clothes in and add an extra rinse to the cycle (Dreft is good, if you're not using this already.)
You could also add an air filter to the room(s) where your baby spends most of her time. This is a good idea on general principle anyway.
More likely than not, she just has a little cold or upper respiratory thing. If she's normal size, you probably don't have to worry so much about RSV or the other nasties, but if she seems to have any wheezing, spikes a fever, etc., call your dr without delay.
Don't be afraid to bother your pediatrician if it will put you at ease...if they didn't want phone calls from worried new mommies, they would have become foot doctors :-)
Congrats on your new baby girl...enjoy her!