My nose is completely clogged and i don't know why. what can i do?

Start simple: First start with a pure antihistamine to see if allergy may be playing a role. Zyrtec, Claritin or alavert are otc and worth trying. If after a few days there is no improvement then try a decongestant as well. If after a few days you are still blocked you should see your family doctor for a prescription nasal spray either a steroid or an antihistamine. If that doesn't help you need to see an ent.

See a doctor: A clogged nose can be anything from swelling for allergies to a mass growing in the nose.