I believe it could be 'turtles all the way down' as the phrase goes. Maybe our Universe started by a collision of two or more other Universes and we got this mess called the Big Bang. This doesn't explain how those other Universes started though.
But then as mere humans, we can't conceptually grasp Infinity itself. This is not some failing of ours, it's actually convenient to not imagine infinity, as it would drive us mad. The minute you include the Infinity Symbol (∞) in a math equation, all logic starts to cease and get very wobbly.