Could he possibly have an ear infection? It sounds to me like you've ruled out him being extra hungry..if he is/was you've taken of that..you're also continuing a comfort for him, which is keeping the same bedtime routine that he's been used too all his little life so far. If it were me, I wouldn't start changing the bedtime routine too much, but look at other things...there are a few possibilities that I'd look at: The ear infection, as the pain can come on sharply soon after laying down (happened to my daughter and she had it in both ears..affected her sleep for 1.5 weeks before I finally took her in to be checked). If it's age related and the world is becoming a bigger, more interesting place and he doesn't want to shut down and go to sleep, perhaps just a min or two of the cuddling, and then working your way through the laying down and reassuring that he needs to go to sleep and he can do it. I have had to do this so much recently, as my dd is getting more and more excited about the world. Part of our bedtime routine has been lullabye music and so she associates it being put on with bedtime and she is going to stay in her crib which takes the guess work away from her..she also has something calming to help her wind down. Have you tried white noise or music? The only other thing that I could think of it, if it's teething pain, perhaps the medicine isn't strong enough to cut the pain? But after 1.5 months I kinda doubt that..if it is though, may he needs something tougher to chew on, or really really cold. I'd try a frozen banana in a mesh feeder for my dd. She will only take it if it's teething pain, and if it's not, she spits it out and throws it down on the ground. There are many options though.
All in all, I bet you and your dh and doing a great job. Hang in there. No one can do it better than you two. Trust your momma gut. Just keep working at ruling out options. Either you'll get to the issue soon, or it'll stop on it's own. Let us know how it goes.