I've had exactly the same thing ever since coming to uni. I've had about 4 weeks cough-free since september, but otherwise it's been me hacking away in every situation. Sometimes it's ganky and very productive (various colours Jamie), other times it's completely dry. Been to the doc's twice about it, both times decided not to give me antibiotics. Instead I got this nasal spray (Beconase) which didn't help at all, and I ended up just having a bit of very dark chocolate before bed to help with the coughing (the cocoa is a natural anti-tussive, and I tended to cough more at night when I laid down).
It's getting annoying now though - all my uni mates think I've got some chronic cough - which, technically, I do - I've had it for 9 months of the last 12. :'(