Nina, your depression sounds much like my chemical imbalance depression. Even on my best days, when I was relatively happy, there was always a dark angel standing at my shoulder saying, "Okay, that's good. But is it so good that if I promise you a pain-free trip to oblivion forever that you would say no?"
So even on the happiest days, there was a cloud, a grayness.
I don't know if you are depressed, but it probably is worth checking out.