Sleep help!

My son is 21 months and since he was born he’s been a terrible sleeper. Just after he turned 1 we did the Ferber method to sleep train him and it seemed to help. We got a few nights where he slept through and went to sleep no problem. Fast forward to around 18/19 months and I feel like were back to square one maybe even worse. He started not wanting to go to sleep unless a parent was present and then now at 21 months he’s been waking through the night and realising we’re not there and crying for us and won’t go back to sleep unless we stay with him which has resulted in one of us having to sleep on his bedroom floor. This has been going on for almost 5 weeks now. I tried the Ferber method again but this made him worse and very distressed. I have noticed he’s cut his last 2 molars but I wouldn’t have thought that would cause sleep problems for 5+weeks?

Any advice would be so helpful!❤️