On a Facebook discussion thread, do I need to cite my source every time I use it (MLA Format).Or is 1 time ok.?

I recently made a Facebook group (secret), as a study group to share information to friends for a cl. My question is do I need to cite my source (MLA Format), or do I just mention the source every time I use it. Also would it suffice if I just put something like "All my sources come from ..... I take no credit for any information posted etc. On the information tab or a discussion thread. I'm just wondering what i need to do to not get in trouble for using someone's work.