[csw]

My daughter had and still has what is called "anxious" attachment..I couldn't put her down, turn my back to her, go to the bathroom by myself without her having to be on my lap..she took six months to sleep at night or take a nap more than 5-10 min..

What really helped me, was practicing attachment parenting techniques..even though Ana was 9.5 months old when I got her home..she exhibited MANY of the same behaviours as in the book The Weavers Craft.

We co-bathed..I carried her in a sling for hours a day..
We practiced therapeutic infant massage techniques,
had skin to skin contact, co-sleep, did adoptive nursing while in Guatemala earlier etc..

What you may need to do with him..is no. 1...treat him like an infant, even though he is 4 years old..
Give him a bottle if he wants it..and hold it for him..
Buy a carrier that goes up to 60 lbs, specifically for older kids..there is the Ergo that goes up to 40 lbs..but there is another one just for toddlers that is up to 60 lbs or more..Ana is over 30 lbs and I still "wear" her..
With the Ergo my back in never sore....
Skin to skin contact..co bath, give him massages..

He has had 2 of his primary caretakers leave..
How hard for him..maybe he is afraid you will leave also..so he doesn't want to get too attached for fear you will leave..

One suggestion, and this sounds strange..is to feed him ice cream while he is on your lap..
The lactose in the ice cream will illicit the same feelings in him that a nursing baby would experience..the bonding etc..