You may use drops to decrease the congestion (decongestant drops) like XYLOMETAZOLINE
for a few days with caution. It is not advisable for a long period.
Along with it you may do steam inhalation before going to bed, which itself has a good decongestant effect.
Further investigation can can be SLEEP STUDY which may cost about 10,000 rupees. If SLEEP APNEA
is diagnosed, which probably is your diagnosis, the best treatment is Continuous Positive Airflow Pressure, or CPAP. It is the gold standard treatment for SLEEP APNOEA.