I have suffered from deep breathing problems for the last 3-4 years. At first, it was only occasionally, and I thought it was s

I can't comment on a possible purely physical cause, jennigens. The tests you've had seem to have covered the most likely physical causes.

It is not uncommon for people with anxiety to either unconsciously vary respiration which produces symptoms of respiratory distress or to perceive breathing problems where there are none. An additional complication is that increased CO2 levels can trigger or worsen anxiety.

Even though Xanax® (alprazolam) is a fast acting benzodiazepine, it may still take 30 minutes or so to become fully effective which is a long time when you are experiencing breathing difficulties. Perhaps continual medication with either a longer acting benzodiazepine - clonazepam (Klonopin®) or diazepam (Valium®), or an antidepressant would be better in your situation. I'd lean toward the latter because benzodiazepines are central nervous system depressants which can affect respiration.

However, IMO, you should initially considering Cognitive Behavior Therapy which can help you develop counters to the thought patterns I suspect are driving these symptoms. Your physician should be able to recommend a CBT therapist in your area.

Best wishes

Ian

NOTE: I am not a doctor, and more importantly, I'm not your doctor so the above advice is necessarily of a general nature which may or may not apply to you. Always consult your health provider before acting on anything you've read here.