Post reminders?...

Below each post you'll see several icons, one of which is a hand with the index finger pointed upwards and a string tied around it. Click on that to add the thread to the Reminder list.

 

Post reminders only appear under "My Home". You can use this feature to remind you about certain posts that you want to come back to for whatever reason.

For example, if a bunch of media posts are made in a day and I don't have the time to download them right away, I'll mark all those posts to remind me. Later when I come back, I have all those posts ready for me under "My Home" for easy access.

Anyway, I'm not sure what you mean by it not reminding you. What are you expecting? If you want notification of certain threads, then mark it as a favorite, and then you can edit your subscription options (under "My Home") to allow for emails to be sent to you whenever a reply is made,