1)To add a comment click right were it says either no comments or a number of comments.
3)When you click to share if your comment doesn't register you may be asked comment with Google Plus. If you do not have an account it will take you right to Google Plus and you can set up your account with in seconds. This could be the reason why you think you left a comment but it never showed up.
-Sorry for the confusion. Thank You follower's! Hope you are now able to comment away.