I have just got the Omega DLC for Mass Effect 3 and it isn't particularly obvious how to start it. I have checked the Galaxy map for any markers and all that is left on my map is the final mission and the remainder of the Leviathan DLC:

I have also tried visiting Aria on the Citadel, but she just provides the normal conversational options from pre-DLC.
Do I need to start a fresh game to access the Omega DLC, or is it that I haven't finished the Leviathan DLC that is preventing me from accessing the new content?
Is there anything else that I am missing?
