Are you on coumadin (warfarin) or any other blood thinners? What is your altitude? Do you have a family history of poor clotting or leukemia? Check ALL of these possibilities. I would also get my sinus passages checked. Lastly, I was exposed to agent orange in Vietnam, and have also had nose bleeds. Have you been exposed to environmental toxins in either or both Gulf wars?
Do you work in a high elevated area? This happens to me on occasion. Maybe you need a humidifier, dry areas can cause nose bleeds as well. There are quite a few sprays that can help if you want to try them, they may require a prescription though. I'm sure there are non prescriptions ones as well at any drugstore.
Some people get nose bleeds every time the weather changes. Others because their blood is too thin. Others just because the house is too dry. Can't tell from what you said. Check the info on your meds to see if that sheds some light on the matter. (my grandson gets a nose bleed just before it rains.)