Click on this .  It should be visible at the top of the screen, even if you scroll. 


You can also click on the Star following comments check box next to the submit button but you have to submit a comment for that to get turned on.   Next time you visit the topic, it will take you to the next unread comment.   Once you follow a topic, the little bell at the top of the page or floating in the lower right corner will pop up to show you that your followed topics have new comments.  

--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.