My 3yo son has asthma& when he sleep at night his nose be stuffed up bad his doctor proscribe a humidifier but to me it don't work for him I think he ne?

Do a Re-evaluation. Unfortunately one medicine/method of treatment does not work for everyone. Your son may have allergies as well, common in asthmatics, and a prescription nasal spray may be of much benefit. I would suggest bringing him in to his doc, express your concerns and I am sure he will be evaluated and treated accordingly. Best of luck..