Why won't this cough go away?

I have this cough that won't go away! It gets to be so bad that I vomit (especially after meals and in the early morning hours.) When I do simple tasks, such as going up and downt he stairs with laundry or playing with my nephew, I begin to cough till I gag. When I recover from it I have a hard time breathing (there's a wheezing noise, too.) I have constant nasal dripping, which has proven too much for my NetiPot. I have been to a doctor and initially he said I had asthma. I told him that's impossible, bc I have no family history of asthma and I have never had respiratory problems (I'm 27 yrs. old.) After an x-ray, he said my lungs were clear and healthy, so he ruled out asthma and chalked it up to allergies (which I also have never had a history of.) He sent me on my way with a prescription for Claritin, Prednisone and an Albuterol inhaler. He said it should be cleared up in about 10 days and to only use the inhaler when I need it. Well, that was three months ago and after the Prednisone ran out my symptoms resumed. Thank goodness for that $55 inhaler, bc I swear sometimes I feel like I'm about to die just going up the stairs or in the middle of the night after a cough attack. I've also been losing quite a lot of weight, bc I'm afraid to eat anything (the coughing and throwing up that ensues after I'm done eating is very weakening.) I don't have insurance, so the only place I can get medical attention is the county clinic where there are nothing but hack doctors like "Dr. Claritin." Please, if anyone can lead me in the right direction as to how I can treat this I would GREATLY appreciate it.