I do not believe that the Bible contradicts itself; hence, whenever I sense a contradiction I call it confusion. Now I am a little confused because I do not know when Jesus became the son of God. This is because some passages of the Bible says he became the son by virtue of his resurrection (Romans 1:4; Hebrews 1:5) while other passages talk about it 'differently.' For instance, John 1:18 talks about the declaration prior to the resurrection. Please sir, kindly make things clear to me. Your usual cooperation is highly anticipated.
"Paul, a bond-servant of Christ Jesus, called as an apostle, set apart for the gospel of God, which He promised beforehand through His prophets in the holy Scriptures, concerning His Son, who was born of a descendant of David according to the flesh, who was declared the Son of God with power by the resurrection from the dead, according to the Spirit of holiness, Jesus Christ our Lord" (Romans 1:1-4).
What Paul is saying is that the power shown in Jesus' resurrection from the dead proved (or declared) that Jesus was the Son of God. He is not saying that Jesus became the Son of God at the point of his resurrection. As you noted, Jesus was called the Son of God long before his resurrection. "He said to them, "But who do you say that I am?" Simon Peter answered, "You are the Christ, the Son of the living God"" (Matthew 16:15-16). Jesus is eternal. He has always been the Son of God. "Jesus said to them, "Truly, truly, I say to you, before Abraham was born, I am"" (John 8:58). And he remains the Son of God. "Jesus Christ is the same yesterday and today and forever" (Hebrews 13:8).
Hebrews 1:5 is a quote of Psalms 2:7. It does not refer to the resurrection. See: Did Jesus become the only begotten of God at his baptism?
I'm highly grateful for the effort put forth for my understanding. I must say I understand the subject more clearly than before.
God bless you.