My Son Is An Asthmatic, And Also Has Hay Fever.

My son is an asthmatic, and also has hay fever. I cannot control the hay fever. He has a constant blocked nose, is on a daily dose of antihistamine and currently using cough meds for a nasty cough that won't go away. I've had him on the nebulizer (duolin and publicity) twice this week and he isn't getting better. What else can I use PLEASE?