S.F.
As a mother of 2 girls, I have found that they are what Dr. Sears termed "high need". There is a wealth of information on this subject on his website askdrsears.com. Also, if this is a recent and sudden change that he has come to live with you, he could be experiencing some pretty significant separation anxiety. As a remedy for my own girls (9 months and 4 1/2 years) we allow them to sleep with us (only the baby is with us now). We found that they sleep better when they know that we are near and that they are not alone. We sleep better because they do. I am not an advocate of the "cry it out method". I think that he really may need some additional comfort and attention. I hope that things improve as the length of time seems to grow.