mild shortness of breath, asthma?

I'm an otherwise heathly 33 yr (F), two years ago my doctor suspected I may have a low-grade asthma due to peak flows she had been monitoring over a fairly long period of time (this peak flow monitoring began after a really bad chest cold where I had some shortness of breath). Other than her suspicions based on the "below normal" peak flow results, I have never had any symptons of asthma; I exercise regularily and have never had wheasing or shortness of breath. I never pursued any further tests as I felt that why bother if I didn't have any symptoms & it didn't seem to affect me in any way.

However, over the past 2 weeks I find myself taking very deliberate deep breaths consistently throughout the day (6+ times an hour). I begin having the feeling that I'm breathing very shallow and require a deep lung-filled breath in order to feel right. Most times I can come up with the full lung full, but about 10% of time I feel like I can't quite get the maximum lung full. This is not really happening while exercised but rather when I'm not doing anything at all.

Are there any other thoughts on what could cause this feeling? Or, if in fact, this is a mild form of asthma that is for some reason progressing, are there any preventative measures I can take to halt this progression? I really hate the thought of taking medications if it is not necessary, but I'm becoming a little concerned.

[National Jewish Health]

These are not symptoms suggestive of asthma and making a diagnosis of asthma on the basis of a peak flow reading is probably not the best way of doing this.  It is still possible that this is due to something in your lungs, such as asthma, or other cause.  Pulmonary function tests (PFTs) that is more than a peak flow measurement will give you some more information.  Other tests may include a chest x-ray.  I would speak to your physician about pursing this problem.