What Causes Persistent Cough?

I have been sick since Feb 14, I was involved with sawing a lot of fine wood on that day. Went to the doctor on the following Wed. had a steroid shot and methyl steroid pack. The coughing continued and I'm still coughing, I am now on day 4 of ampicillin 875 mg and I am clearer this morning. One problem is I have coughed so much I am sore under the left rib cage especially, Also am doing breathing treatments 3 to 4 times a day and have a prescription cough medicine.