HI S.,
I don't have a lot of advice, but I do have 3 kids (13, 9 and 17 months). My first two were sleeping through the night by 3 months. My son however, 17 months, was a different story. He was sleeping through the night early on, and then stopped. But, at about 10 months or so, I had enough. I knew I could get him to sleep through, as he had done it before. So, I did read some helpful 'sleeping' books I got from the library. I can't recall what they were though, but most recommended a routine. Do you have a routine at night? Whether it's a bath, or a story, or rocking in the chair? What I did was what some might think is harsh, but I started to put him down awake in his bed at night after a drink of water and rocking in his chair, I'd cover him with his blankey, and tell him "goodnight I love you" and I'd leave the room and close the door (not tight, but it looked like it was shut). At first, he cried! But, only for about 20 minutes. Then he woke at 1am. I did not go in, I layed awake listening to him cry for about 40 minutes (on and off). then he went to sleep. yeah! The next night, same thing. He took his bedtime better--just a little cry and he was out. He woke at 1--cried for 10 minutes, went back to sleep. And, he has slept through the night since. Now when I put him to bed at night, I tell him it's nigh-night time, and he grabs his blankey, blows kisses to everyone and walks to his room! It still shocks me every night. :-) We do a little drink of water, rock, I tuck him in his crib and rolls over and goes to sleep. Probably doesn't happen for everyone, but it worked for me. From what I read in the books, it could take much longer since your son is older. May take a week, but if you stay firm with what you want, it will happen. :-) Good luck to you!!
J.