Help for Hay fever cough?

I am asthmatic and over the last couple of years have developed a hay fever cough. I have had tests to check it out and the doctor has given me several types of antihistamines, non of which seem to work very well. They seem to work for a couple of days or even, in the case of the last lot, a few weeks then they stop. My chest is very tight and hurts. I already have a steroid inhaler and a salbutamol one but they don't seem to help either. Anyone any ideas what I can do to get some relief.