That is a common theory/accusation.
If you'd like to refute it, I think you have to explain why it's OK to lack any theory about how God came to be (or why he's always existed) but it's not OK to (more simply) lack a theory about how reality came to be (or why it's always existed)
When you say "reality" do you mean the universe?
I mean reality - that which exists. Nature. I would call it God, but I believe you insist that God created Nature, so that might not make much sense for you.
I think that's just another name for the universe, and I can see why you'd want to avoid using that term, given the Big Bang and all...