Most probably it may be due to cold, sinus infection. It may also be due to structural abnormalities, such as septal deviation, concha bullosa and adenoid hypertrophy. Check with your doctor. To relieve blocked nose due to cold,
Add 1 tbsp of carom seeds (Ajwain) to a bowl of boiling water and inhale the steam.
Keep your head elevated.
Drink lot of water.
Use a cool mist humidifier.
Use over-the-counter saline nasal sprays.
Use a menthol cream on your chest.
Use over-the-counter adhesive strips that help keep your nostrils open.
Suck on a cough drop that has menthol in it.