Re: Never ending cold....what meds?
It sounds like it could be airborne allergies. He could be breathing something like dust mites in your house and reacting to them. Additionally, childhood asthma is mainly allergy-induced.
The first allergy test I took came back negative for everything. My asthma symptoms still persisted. I got tested again by a different allergist and reacted severely to a number of things. I'd suggest getting him tested again - there are a few different methods of allergy testing.
Another idea is acute or chronic sinusitis. My suggestion would be to get a referral to an ENT (ear, nose, and throat specialist). Even the sinusitis can be allergy-induced.
As for antihistamines, Zyrtec is one that's safe for asthmatics. It's by prescription only though.