constant chest tightening and shortness of breath

I am having very uncomfortable chest tightening (not painful) but enough to shorten my breaths stop me in my tracks and at times change the pitch of my voice for a second. I have no other symptoms except headache after a long day of trying to breath. I have had this for about 8 years and have had EKG that's fine. It will go on all day not stopping for a moment...even had it last night in bed resting...felt like there was a truck on my chest. Its very aggravating. I may have it for a week at a time...then it goes away for 2 weeks then is back again for a week. I have been diagnosed with asthma and have asthmacort and pro air....these do not seem to help at all! I do not smoke, I am not over weight, and consider myself active and fit (not as much lately due to breathing issues). I have ALOT of stress in my life but I cant imagine these symptoms happening at night while I'm sleeping if its stress. Any ideas? I think my doctor is at a loss as well