My son has been suffering from post natal drip which causes non stop dry cough . I was told to use the pediatric sinus rinse and I had been using fr a

My son has been suffering from post natal drip which causes non stop dry cough . I was told to use the pediatric sinus rinse and I had been using fr about two weeks . Every time I rinse his nose the will be a thick yellowish mucus .Is this normal ? His cough has been reducing but I still continue rinse .How long should I continue using the product.