If 'god' is a metaphysical term, then it cannot be even probable that a god exists. For to say that 'God exists' is to make a metaphysical utterance which cannot be either true or false. And by the same criterion, no sentence which purports to describe the nature of a transcendent god can possess any literal significance.
Where did God come from? If we decide this is an unanswerable question why not save a step and conclude that the origin of the universe is an unanswerable question.