i wrapped my bubs from the day they were born, both were happy with it until about 8 weeks where they would get frustrated at not being able to move their arms so we stopped then.
I didnt have a sling with DD1 but DD2 went into her sling the day she was born and has always loved it. What kindof sling do u have? if it was a one shoulder type, maybe ur DS didnt like to lie down and would have preffered something like the HAB, CC or ergo where he was upright?