Could This Be the Beginnings of Asthma?

I'm wondering if it's possible to develop asthma at the age of 45.

I've been experiencing a few symptoms over the last year or so which i'm a bit worried about - I know I should go to a doctor, but I thought i'd see if anyone here can help first.

I've often got a tight feeling in my chest, with a dull pain (like my bra's too tight.) I sometimes feel a bit breathless, and sometimes have a bit of wheezing. I feel like my stamina isn't anywhere as good (i feel exhausted after walking for half an hour, when before, I could walk all day!) I sometimes cough up some very sticky mucus, too.

My blood pressure is normal (so i'm not worrying about my heart) and my weight is normal, but I don't smoke. I work across the road from a demolition site, which has produced a lot of dust in the last few months. My job is pretty stressful, too - i'm aware that stress can cause all sorts of weird problems, too.

Any ideas? Thanks in advance...
Oonagh.