Yanno, the thing with slings is, you usually try them when baby is crying and irritable (cos that's when you are desperate) The crying escalates as you fumble trying to get it to work. Change tack! Feed, pop in a sling in the brief time he is happy - go for a long and quick walk. An upright sling will work better than a ring sling. But walk, walk, walk. When he learns to associate sling with sleep life will be easier. You are doing great