You want to know: "If there is God, who created God?" Good question!
To ponder the creation of God can only lead to pondering the creation of that entity which created God. Sooner or later one has to conclude that there is a source that has always been, one without beginning or ending; a creative source that is existential. The Urantia Book calls this reality "the first great creative Source and Center of all things and beings."
Because all finite human beings have a beginning, it becomes nearly impossible for us to comprehend any reality that is without beginning or end. Such a reality as God is by definition then, Infinite. Just as surely as a finite reality exists, an infinite one does also. In fact, it makes perfect sense that only an infinite reality could bring finite reality into existence, the finite reality being but the shadow of the greater infinite reality.
There's a great deal of evidence supporting the existence of God for anyone honestly seeking to find God. Ironically, it's not evidence that can be offered to anyone as conclusive proof. The existence of God can only be validated by each individual's personal experience with God and such experience comes only as a result of reaching out with faith to find him and to know him.
Your question is a good one, and a question that might lead to very deep thought, as we ponder the mystery of God...but deep thought is always a good thing, and this subject of God is one that is certainly worthy of such thought...we will never reach the end of our quest for the truth of God!
Thanks so much for asking; I hope that this reply has been helpful.