I love love love CK - it's the one thing that I always use. Everything else I experiment with - but I use CK every time. It really helps with the frizzies, and I don't get anything negative with it. I even use it alone after a DT.
On a side note, I've had the same issue at various times in the past, and for me, it turned out to be 1. buildup and another time: 2. protein sensitivity. And of course there's always 3. overconditioning. You've probably already gone over all of this, but just some food for thought if not.
Hope you figure it out! My fingers are crossed...