Go your cp and read down the list on the left, click on "Edit options" underneath the heading called " Settings and Options"
when that opens Look under "default thread subscription mode" and choose via the drop down - an option for subscribing to threads - whether you want to be notified by email or not and how often if you do want to be notified by email - it sounds like yours is ticked right now at "do not subscribe"
you can also look on the toolbar above where it says thread tools, click the arrow down and select subscribe to thread (if you want to leave the default to do not subscribe in the automatic mode from your cp)