I know exactly what you're going through - although in reverse!! DS2 has never been able to settle himself (he is now four months old) although ATM he is doing a lot better than he was in the first six weeks. From what I've read some babies are born not knowing how to settle themselves. I didn't know this as DS1 was the complete polar opposite to DS2. DS1 always settled himself and was a dream.
What I found helped me during the day was to either rock him in a rocker (or bouncinette) and just lately the pram and then transfer him to his cot. At night he usually settles himself although in the first few weeks in the wee hours I would bring him into bed with us so as I could get some shut eye lol. Have you tried a dummy, perhaps slipping it into his mouth just as he is starting to fall asleep and then putting bubs back into the cot?
Also read up as much info as you can regarding this, I can highly recommend a book called "100 ways to Calm the Crying" by Pinky Mckay. In that book there are heaps of different techniques used to help you to learn how to settle bubs.
Melanie, Qld, Joshua J 18.04.02 & Jacob M 04.10.03