If you are not seeing a counter against "Alerts" in the top line when someone responds to your posts, then:
- Open the Settings option within the Alerts pop-up at the top of the screen (or the Notifications one under your name).
- Look for the preference option "How frequently to tell me:" and set it to something useful. ("Immediately (but only for the first unread message)" is a good one.)
- Look for the "Notify me of:" preference option, and set it to something useful. If you want to see notifications of "Likes" then make sure "replies" is included in the one you choose.
- Scroll to the bottom and click on "SAVE SETTINGS"
That should fix things.
Note that the counter will only show a count of "un-read" alerts. The system will automatically mark alerts as read (and so no longer count them) if you visit the page with the response on it. You can, however, see all the alerts you've received, whether read or un-read, by clicking on "ALL ALERTS" in the Alerts pop-up.
I think what's happened is that there are some new notification options in this version, and, depending a bit on how you had things set in the previous version, the way the settings from the previous version have been translated sometimes leaves the new settings in a slightly strange state. The instructions above should cover getting them back into a reasonable state.