You should definitely see your primary care doctor
about this issue. Nasal stuffiness and difficulty breathing is a very common problem, but when it goes on for so long (as it has in your case), it really needs to be checked out. Many times the cause of the problem is something that can be fixed and there is no need to go on suffering with it!
First of all, your doctor will rule out nasal allergies (called also allergic rhinitis). This is a very common problem, often provoked by various indoor allergens like mold or mites (which might be concentrated in the bedroom, hence explaining why the symptoms are worse at night). If your doctor diagnoses you with allergic rhinitis, they will be able to suggest one of several very effective medications, including anti histamines and nasal steroid sprays.
A deviated nasal septum is also on the list of potential causes, as are nasal polyps. Both of these conditions will produce many of the same symptoms as nasal allergies, such as congestion and 'mouth breathing'. If your doctor takes a look in your nose and finds a deviated septum or polyps, they will likely want to refer you to an ear, nose, and throat (ENT) specialist for possible surgery