Besides saline nasal drops , steam inhalation is good to relieve the congestion due to phlegm .   You could keep the baby in your lap and try to get humidified air through a steamer kept near both of you . You can also achieve this by running a hot water shower in the washroom and sitting with he baby a little away from it in the closed bathroom .  This humidifies the air passages of the baby and softens the phlegm . After that you can put the baby down on his tummy and gently pat the back of the baby with your cupped hand to move the loosened out phlegm so that he may either cough it out or swallow it     In very small babies we try to avoid decongestant  medicines .     But if your baby has fever , has breathing difficulty with fast chest movements, has excessive crying , vomiting , non acceptance of feeds , it warrants a trip to the Pediatrician for a physical evaluation to rule out chest involvement in the form of pneumonia

this can occurs due to weather changes and temperature variations or simple cold and rarely infection. kindly give nasal saline drops (nasoclear /nasivion s)every three hourly and since it is a salt water/saline water it does not have any side effects and can be given again and again for nasal blockage and respiratory cough. it will dissolve mucus in nose and throat. for fever and pain give paracetamol. anti-cold medicines at this age have got side effects so can be given only after medical consultation. try to prevent temperature variations around the child and you can also give indirect steam inhalation and if there is no improvement in 2 or 3 days then meet your doctor 

Pls go for in clinic consultation

Ur baby is only 1.5 month old Better to continue with nasal drops And show ur nearest pediatrician once for detailed examination