How to ensure that I am not starting a discussion that is already discussed ?

No. You can also "Refresh" an older discussion, because as soon as You make a post in it: it appears in the LIVE STREAM, and thus catches the attention of others. How to ensure this one? There is an option like...SEARCH? Use that one, it will find many similar titled topics and express Your thoughts in it! We surely will join You as well...or might join. :P I would advice You to start only very specific discussions. For example, Your friend has told You something: and now You do not know how to react: A or B way? So then start a discussion about it here, and we might help You to understand what most of the myLot members would prefer to do or say in Your place.

Ou, and also I like to look after the discussions that my friends have started or participated in. So this is another way how to catch an interesting discussion!