I went through the blue fog in act 2, when you pass through the undead army. However I want to return to the other side. How on earth is this done? Suggestions?

Did you finish what you had to do when you past the other side? Dunno if you have to though, but if you don't know where you go you just go to any place of the map where there is fog and wait for a few seconds till you teleport to the battlefield.

That doesn't quite address my problem. It sounds like you're describing how to enter the battlefield. I'm trying to get back to the camp on the other side of the fog. Originally when I went past the fog/mist, away from the camp, I used my medallion to lead the way. Now I want to head back to the camp and I'm unable to do that. The medallion won't direct me back. I have no idea. Regarding your question, I am not sure if I did everything I need to on the current side of the fog. I am just trying to follow one quest at a time.

The medallion should still work. However, Alchemistlord has a good point for you to consider: you must have done everything you need to do before trying to return.

If you're using the medallion, you're on Roche's path. So be absolutely certain sure that you have the standard of the Dun Banner (from the ghost, in the catacombs), Vandergrift's sword (from Saskia, in the mine), and Yahon's spearhead (from Skalen, at the gate). Do not try to return until you have all these things.

Fantastic. Thank you very much.