I take it that "the universe is endless" means our universe undergoes cycles of expansion and contraction, birth and rebirth (because the universe is still expanding according to our latest theory that has been supported by observations).
The common response you'll get for "Who created God?" will be something like "He's beyond our understanding, so we don't question where He came from because we will/can never know". It's faith as Pedobear cited.
I am an agnostic who believes there is a higher being but doesn't follow an established religion because of that ignorant and vague explanation of God's origin. You can say I'm sitting on the fence and that my approach will be "when you discuss science, don't bring up God". For me, science is about using what we know to explain phenomena, not invoking something/someone that we can only believe exists without further support apart from conjectures and speculations. I no longer have a strong belief against "God" but I don't cite "God" in explaining something.
In science, apart from mathematics-related areas, I was taught not to "prove" a hypothesis, but only to "support" or "refute" it. That the experimental designs give overwhelming support for something doesn't mean it can't be overturned later. That something as wonderful as quantum mechanics has in it many mysteries kind of amuses me when I study it. There are just things you should not ask, or bother to ask in quantum mechanics. It's sometimes nicked "shut up and calculate" physics (but don't take it literally).
You may be interested in
The Flat Earth Society that advocates biblical descriptions of the world by turning the modern scientific tools onto themselves (Einstein will rise from his grave if he read what they did to his relativity). Marvellous minds in the wrong can of thoughts. Seemingly convincing but fallacious at its core. Read and don't fall into their trap. It looks real. You just have to know where it's wrong. Enjoy.
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