It is not clear from what you have written as to the cause of the coughing you are experiencing. It could be bronchitis from an infection, chronic bronchitis from smoking daily for 5 years, or an exacerbation of your asthma. It should be fairly easy for your physician to tell the difference and prescribe accordingly. You need a good physical examination, probably a lung function tests and possibly a chest x-ray. I would suggest seeing your physician as the first step.
nick, try doing the Buteyko Breathing exercises, that's what finally got me on the road to recovery with my own respiratory problem. There's a couple of great books by Patrick McKeown, both available on Amazon, "Asthma Free Naturally" and "Close Your Mouth". Close your mouth is basically a mini-version of Asthma-Free, both will tell you how to do the exercises but asthma-free has more history on Prof. Buteyko and the reasoning behind why the exercises work. You can also find a little info online at these two pages:
http://members.westnet.com.au/pkolb/but_strt.htm
http://www.btinternet.com/~andrew.murphy/asthma_buteyko_shallow_breathing.html
Know this, your body has the innate capacity to heal itself. Give it time and good support. Try to eat well, lots of fruits, veggies, and try to stay away from refined sugar (it's a killer to your immune system). More diet and supplement advice in the Asthma-free book. Good Luck!