Whenever i feel short of breath i panic. i have been tested for asthma and have had lots of ekgs. but am almost constantly sob...what could it be?

Many things: Panic can give you shortness of breath and vice versa. A number of young women suffer from vocal cord syndrome, where their vocal cords contract and they cannot breathe. I wonder if you have been tested for that? See a good pulmonologist.

Anxiety?: There are many conditions that are associated with a sensation of shortness of breath. It is best to continue to work through your physician to clarify other etiologies besides anxiety. For a list you can go here: http://www.Mayoclinic.Com/health/symptomchecker/ds00671/symptom=308fdbb7-2a5d-9994-ed771d8e406680c0&tab=shortness%2520of%2520breath.