A.C.
If he was sleeping through the night before then you know with certainty that he can do it (i.e., he doesn't need to be fed, etc). I would give it 2 nights without going to him when he wakes. If he cries, try hard not to go to him (obviously only if you're sure he isn't sick) and I am betting within that time he'll go back to sleeping straight through the night (worked for me with two kids, anyway). Also, put a bunch of pacifiers in his crib so he can easily find one when he needs it.