Sorry but I can't offer any solution but I can say that you are not alone. My now 22 month old son has the same problem has always been such a good sleeper, about 3 months ago he had a bout of gastro which seem to upset the apple cart. It took 2 week s to get his day nap (2hrs at lunchtime) back on track. Night's are a totally different story. He had been sleeping in our bed every night, sometimes at about 10-11pm and sometimes we had to go to bed to get him to sleep with us. I tried the contolled thing and just couldn't do it. Have also thought it was his teeth, only has one molar to go, but this week we seemed to have realised something, he will go to sleep in his own bed (yes, we even bought him a single bed to try and replicate ours)when there is only one parent around. So for the last 3 nights my partner has put him down while I have gone and hidden my self quietly in the study, and it has only taken 3mins for him to fall asleep (no crying or tantrums), so hopefully this is him out growing this sleep problem.
I hope your son outgrows his problem soon as it becomes more of an issue.