C.R.
Put the shirt you wore that day or night in the crib with baby...It sounds gross but wrap him in the shirt or use it as the blanket....it smells like you and it will comfort him...if you have a musical stuffed animal play the music when you are with him and then someone else can play it when you are gone to relax him...babies have no reference of time or place so when he can't see you he doesn't understand you are comming back(that's why peek-a-boo is so fun)...if he's still in the room with you maybe now is the time to move him...good luck!