What Causes Shortness Of Breath?

I can not breath, I m about to die. This has been going on for a couple of days. I have been working in my yard the last week. I have been taking benadryl allergy medicine and something called Mucus Relief, then I ran out of benadryl and I went to the drug store and and got some Bronkaid. That helped after about 30 mins. but now it doesn t seem to help. When I try to swall. I choke. I am cont. to cough and cough and that hurts my hemiroids (sp) I m 74yrs old and have a rare blood disorder---polysithema Vera. I m on interferon 3,ooo,ooo units once a week -it seems I can t spell anything, either.