Check your junk folder as sometimes things get sent to junk by accident. Also if you go to settings as baooozs suggests (or "quick links" on the top menu bar "subscribed Threads"), go to the bottom, right of the screen (under the list of subscriptions) n make sure that you have "subscribe by E-mail" checked n not "control panel" if subscribe by E-mail is ticked then to the right of every subscribed thread it should say "instant"
Hope that helps.
Evey