I have a blocked nose every night what can this be?

Allergies. A common cause of nasal congestion is allergies. Allergen avoidance through the use of a dust mite pillow case and mattress cover, as well as an antihistamine like Claritin or Allegra may all be helpful.
It all depends. It could represent perenial allergic rhinitis with sensitivity to dust mite, animal dander, or feather depending on your environmental history. During the winter months, it could be related to dryness in the bedroom. It may also relate to the fact that gravity moves secretions to the dependent side of the nasal cavity giving unilateral nasal congestion.