this may actually be something you were born with. we are all asymmetrical in one way or another. women are more aware of this than men, for obvious(to me, being a mammal and all) reasons.
have you talked to an ear, nose and throat guy? not to seek treatment so much as to get the opinion of someone who has seen a lot of nostrils. if it bothered me , thats what i would seek - experience. there may also be some good info and pictures on the web these days. google ear, nose and throat or simply ENT or a combination of those and nasal passage or blockage, etc.