Why am i coughing and wheezing?

[Bananapeal]

Hi! The past year I've been coughing a lot. Mostly dry, but sometimes with mucus. The coughing appears in the morning, after exercise, and when exposed to certain irritants such as dust and cleaning sprays. Sometimes I cough at night.

In addition I've been experiencing slight wheezing/squeaking at night, when laying down. This has usually appeared following exposure to irritants or after exercise. However, lately, now that it's colder outside, I've had the wheeze every single night. Additionally, I've been wheezing straight after exercise, which is new to me. The wheeze is only when I breathe out. I can't hear whether it's coming from my throat or lungs, and I can't feel it at all. I can only hear it?

I'm not experiencing any difficulty breathing, or shortness of breath. I am, however experiencing a lot of post nasal drip, which I have had most of my life. I'm allergic to dust, mold and grass. Not taking any meds at the moment. Never smoked. Mid 20s.

So I'm wondering, although it sounds a lot like asthma, could it be something else?

I've been to the doctors (before all the wheezing started). Did spirometry, which was negative. I have a peak flow thing (had asthma when I was a kid), which is mostly within 90% of personal best, even after exercise. It only gets really low when I have a cold.

So what could it be (except asthma)? Could it just be the post nasal drip? Is there any other possible explanation?

If it is asthma, is it bad if I leave it untreated? It's not affecting my day to day life, nor am I having trouble breathing.

Hope you can help!