"why can't God be conscious of Himself?"

Because if he is only consciousness, that's impossible, because consciousness cannot be conscious of itself. Just as an eye cannot see itself or an ear cannot hear itself.

"I am conscious of myself and even of my own consciousness."

You are conscious of the things you are conscious of. You can even be conscious of the FACT that you are conscious. But if all the things that you are conscious of were removed until none of them remained, there would be nothing left, not even the consciousness. Consciousness needs something to be conscious of, just light needs something to illuminate.