Since you mentioned dry and unproductive Caleb and I always get an asthma cough with resp. stuff and nothing really helps unless we're using albuterol. It took me a long while to figure that out with myself because it was adult onset for me, it is the only time I have asthma, and it's entirely cough variant - no wheezing or the like. But the albuterol helps immensely.
People swear by Mucinex and I think it's worth a try for sure. It doesn't help me when it's an asthma cough of course. Honey is better than cough syrups for coughs with kids. I suspect adults would be the same. http://health.usnews.com/usnews/heal...kids-cough.htm
Also, I know doctors gave me a prescription something once. It worked wonderfully for my friend who used it and my own husband. I think my issue was asthma (unkown then) and so it wasn't great for me. But I know there are (or were) prescription options for really desperate situations. And five days with a dry cough keeping a person awake sounds desperate to me.
No fever or other symptoms, right? I mention because my sister had viral pneumonia and it was a dry cough that kept getting worse. I didn't know pneumonia could be a dry cough but it can. And I know that the H1N1 flu seems to be producing viral (rather than the more typical post-flu bacterial pneumonia).
I hope he's better and sleeping well soon.