I recall reading a thread on boards.ie in which loads of people had the same issue - I certainly do with mine. Apparently the solenoid valve (sp?) needs to be replaced in them after a while. Yours being only a couple of months old will still be under warranty - get on to wherever you bought it or if your plumber supplied it get him back to replace the valve.
P.S. Mine stops dripping if you kind of 'snap' the shower off - i.e. turn it off sharply when you're finished.