Sleep Troubles

My son hasn’t really slept through the night and is 15 months now. At Thanksgiving time, we finally did CIO against what I wanted because he was up 3-4 times a night and we suspected it was reflux and they wanted to do a scope at Children’s. When I found out what that entailed, we chose to do CIO. It took two days and worked like a charm. He came off all his meds as was totally happy and healthy. I had two weeks off for Christmas and he was still doing great (6 weeks of sleeping all night and going to bed pretty much as soon as he went into his crib). The night before I went back to work from break (three nights ago) he cried and cried. We went up once with Tylenol and water and kept crying. Ever since then he is up multiple times a night again, cries and won’t nap when we can tell he’s exhausted, and won’t fall asleep without crying for forever. What do I do? No sanctimommy bs is needed.