The relative humidity is much less these days rendering the air dry and hence causing a lot of airway irritation and the drying up of secretions causing nasal blockade.
Give bath daily to your child.
put up a normal steamer and keep it in constantly for 3-4 hours near the child but not in front to avoid scalding burns.
Also put saline nasal drops 10-15 times a day to relieve the nasal block. you can also wash inside nose with luke warm water with a pinch of salt.
Ask your pediatrician for some anti histamine syrup for symptomatic relief.