We moved several times starting when DS was about 16 mos old. It did seem like there was usually a rough patch that was worked out within about a week. If I remember correctly, I'd have to go in and do some very careful soothing him without picking him up (trying to avoid anything that could become accidental parenting! although sometimes I did wind up sleeping in the room for an hr or so, when I woke up I'd leave), gradual withdrawal and gradually it got to the point where I could just comfort him outside the door. Then the problem stopped! Good luck!
p.s. I think we may have also started talking up how nice his room was, where everything was, etc. at that time, trying to help him process where he was, etc.