What does it mean for Israel's God to have a "Son"? Is this to say that Paul and the other New Testament writers give some credibility to pagan concepts of fertility and procreation in the celestial realm?
Check out some commentaries on the OT passages that provide the background for this usage. For example:
Example of books that deal with this topic:
D. A. Carson has a small book that might help you with this question: Jesus the Son of God: A Christological Title Often Overlooked, Sometimes Misunderstood, and Currently Disputed.