OK, glad to be of service.

I would say that it would be wrong to say that nothing in the Psalm applied to David, but it seems clear to me that it is a Psalm about Christ.
Here's Spurgeon's take on this Psalm.
[quote:8ee1592366]SUBJECT. This is beyond all others THE PSALM OF THE CROSS. It may have been actually repeated word by word by our Lord when hanging on the tree; it would be too bold to say that it was so, but even a casual reader may see that it might have been. It begins with, "My God, my God, why hast thou forsaken me?" and ends, according to some, in the original with "It is finished." For plaintive expressions uprising from unutterable depths of woe we may say of this psalm, "there is none like it." It is the photograph of our Lord's saddest hours, the record of his dying words, the lachrymatory of his last tears, the memorial of his expiring joys. David and his afflictions may be here in a very modified sense, but, as the star is concealed by the light of the sun, he who sees Jesus will probably neither see nor care to see David. Before us we have a description both of the darkness and of the glory of the cross, the sufferings of Christ and the glory which shall follow. Oh for grace to draw near and see this great sight! We should read reverently, putting off our shoes from off our feet, as Moses did at the burning bush, for if there be holy ground anywhere in Scripture it is in this psalm.
DIVISION. From the commencement to the twenty-first verse is a most pitiful cry for help, and from verse 21 to 31 is a most precious foretaste of deliverance. The first division may be subdivided at the tenth verse, from verse 1 to 10 being an appeal based upon covenant relationship; and from verse 10 to 21 being an equally earnest plea derived from the imminence of his peril...
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I know that the Lord watches over all His children's ways, even from the womb long before we ever come to a saving faith. This must be balanced against the other verses showing that all Adam's children are born in sin and need salvation. In my humble opinion, it is a stretch to say that faith in an infant is a normative truth because of other Scriptures that teach otherwise.
[quote:8ee1592366]Genesis 6:5
The Lord saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually.[/quote:8ee1592366]
[quote:8ee1592366]Romans 3 v.9 What then? Are we Jews any better off? No, not at all. For we have already charged that all, both Jews and Greeks, are under sin, 10 as it is written:
"None is righteous, no, not one;
11 no one understands;
no one seeks for God.
12 All have turned aside; together they have become worthless;
no one does good,
not even one."[/quote:8ee1592366]
No exception is made for Covenant children. Jesus said he came to save the "lost sheep of Israel". Matthew 15 v. ." 24 He answered, "I was sent only to the lost sheep of the house of Israel." If they were born saved, there would have been no "lost sheep" to save.
Continuing with spurgeon:
Verse 9. "But thou art he that took me out of the womb." Kindly providence attends with the surgery of tenderness at every human birth; but the Son of Man, who was marvelously begotten of the Holy Ghost, was in an especial manner watched over by the Lord when brought forth by Mary. The destitute state of Joseph and Mary, far away from friends and home, led them to see the cherishing hand of God in the safe delivery of the mother, and the happy birth of the child; that Child now fighting the great battle of his life, uses the mercy of his nativity as an argument with God. Faith finds weapons everywhere. He who wills to believe shall never lack reasons for believing. "Thou didst make me hope when I was upon my mother's breasts." Was our Lord so early a believer? Was he one of those babes and sucklings out of whose mouths strength is ordained? So it would seem; and if so, what a plea for help! Early piety gives peculiar comfort in our after trials, for surely he who loved us when we were children is too faithful to cast us off in our riper years. Some give the text the sense of "gave me cause to trust, by keeping me safely," and assuredly there was a special providence which preserved our Lord's infant days from the fury of Herod, the dangers of travelling, and the ills of poverty.
Verse 10. "I was cast upon thee from the womb." Into the Almighty arms he was first received, as into those of a loving parent. This is a sweet thought. God begins his care over us from the earliest hour. We are dandled upon the knee of mercy, and cherished in the lap of goodness; our cradle is canopied by divine love, and our first totterings are guided by his care. "Thou art my God from my mother's belly." The psalm begins with "My God, my God," and here, not only is the claim repeated, but its early date is urged. Oh noble perseverance of faith, thus to continue pleading with holy ingenuity of argument! Our birth was our weakest and most perilous period of existence; if we were then secured by Omnipotent tenderness, surely we have no cause to suspect that divine goodness will fail us now. He who was our God when we left our mother, will be with us till we return to mother earth, and will keep us from perishing in the belly of hell.
http://www.gospelcom.net/eword/comments/spurgeon/psalm22.htm