I'll assume you're competent enough to have already tried washing your sinuses of tissue irritants, oh wait, you're posting on here, never mind. Try washing your sinuses of tissue irritants. If that doesn't help it's probably histamine being released from a mast cell in response to something in your environment which should feel like a burning sensation in your nostrils so take some Benadryl or a nasal spray like Cromolyn and try throwing out your new collection of tear gas grenades or whatever could be upsetting your nose.