epistaxis (nose bleeds) can have mulitple causes from irritation of your nasal membranes from allergies or colds to just dry air. less-common people who tend to bruise or bleed easily are likely to have more nosebleeds. taking a daily aspirin or any medicine that is known to interfere with blood clotting can cause them. your first step is to read about nosebleeds. webmd has some great information. next you need to know how to appropriately stop a nosebleed (many people think they do but are doing it wrong). nosebleeds that are frequent and from the same side of the nose can be chemically-cauterized by your medical provider. in most cases this will fix the problem.
i have had nose bleeds at least 4 times this year alonei do not have a history of nose bleeds other than hitting my nose