people who smoke weed and cigarettes and don't stop when they get sick are going to occasionally get a cough just like you describe, i've had it before, it sucks. if you go to the doc and tell them you are a smoker they'll probably give you something, i usually just tough it out. this used to happen to me with low quality weed, huge bong rips, and cigs. since i started smoking better quality weed it hasn't happened in years, knock on wood.