Go to MyFlyerTalk, then click "List Subscriptions" in the control panel on the left. Check the notification type in the list. It may be set to "no email notification." If it is, check the box at the top right of the list, to check all the individual subscriptions, and change the notification type via the "Selected Threads" pull-down menu at the lower right of the list. If you don't want the same type of notification for all your subscribed threads, check them individually or in groups and do the same.
A second possible culprit is that FT has an old e-mail address for you and it doesn't work any more. Go to "Edit Email & Password" in the control panel to check that.
If the notification type is already set to something else, you're sure there have been posts in at least some of your subscribed threads, and your e-mail address is correct, please post here again. Someone will think of more possible reasons.