Maybe a thread which you posted in previously and therefore were automatically "subscribed" to has become active again? If it is no longer of interest to you it is easy to "unsubscribe" from it.
Go to the word "Settings" (at the top to the right of where it says "Welcome, Maryrav") and click on it
Then click on "View all subscribed threads"
You should then see a list of threads you posted in and were subscribed to.
Select the ones you want to unsubscribe from by clicking on the empty box at the right beside the thread titles.
Then scroll down to the bottom where you will see on the right of the screen the word "Selected Threads" with a little downward triangle beside them.
Click on that box and a menu will open where you can choose "Delete Sunbscription" then click on the "Go" box.