Asthma, coughing, and throat clearing

I have had a cough for years now but in the last two years it has gotten much worse and is accompanied by nearly constant throat clearing.

The doctor says it is asthma. If so, what is causing the asthma? The air quality in our area is not great but it is certainly not LA either.

I see several possible causes:

1. GERD (aka heartburn, acid reflux)
2. Food allergies
3. Airborne allergies

I eat junk food, food that is spicy and high in fat, too fast, too late at night, and too much.

I believe GERD to be the primary culprit.