It's an official dogma of the Catholic church that God's existence can be proved by the unaided reason. Did your Catholic education somehow omit any mention of the Five Ways?

http://www.ewtn.com/library/councils/v1.htm

>If anyone says that the one, true God, our creator and lord, cannot be known with certainty from the things that have been made, by the natural light of human reason: let him be anathema."

I am not a Christian, and I'm certainly not going to start defending Catholic arguments for God's existence here (!), but the arguments definitely exist.