I can't breathe though my nose any more. What can I do?

Since there are many reasons people can have difficulty breathing through your nose, you'd best be served by an "in-office" evaluation and examination by a nose and sinus specialist to ascertain the root causes and come up with a solution for you.  Best of luck.

Difficulty breathing can be caused by swelling of the
soft tissues on turbinates usually from allergies, airway obstruction from a
deviated septum, fractured nasal bones, polyps or large bony prominences from
the turbinates. Soft tissue swelling can
be treated by reducing exposure to allergens, and medications such as antihistamines
and steroids. The other listed problems
need to be addressed surgically. Best of luck,
Dr. Michael OmidiAn in-person exam with a
board-certified plastic surgeon is the best way to assess your needs and
provide true medical advice. The response to the question does not constitute
a doctor patient relationship or formal advice.

There are many reasons for not being able to breathe through your nose.  Generally speaking, they can be divided into 2 categories: mucosal disease and structural obstruction.  Mucosal diseases are caused by changes to the inner lining of the nose (for instance allergies) and are usually treated medically, meaning no need for surgery.  On the other hand, a structural obstruction is usually caused by either your own normal anatomy (like septal deviation) or abnormal mass (polyps, tumors for instance) physically blocking the nasal airway; the treatment for this may be surgical.I recommend that you seek a board-certified nasal specialist who can examine you thoroughly and decide the appropriate treatment.  Good luck!