My DH had a mild case of this for a while when DD2 was little. I was busy having carpal tunnel problems of my own at the time, so I didn't really pay it too much attention. I think he managed to sort his out by positioning his arm/hands differently when he was doing stuff (like holding DD) and it just kind of went away.

Is there a physiotherapy service at the hospital where you had DD? Maybe they could help you out with a wrist guard?