Putting baby to sleep....HELP

My son used to go to sleep by himself bed time & nap times. All I would do is put him down and leave the room. I might of had to go back in once or twice but he was so easy.

He is 11 months now and the last 3 weeks or so he wont go to sleep in his cot. He cries and sits up and gets hysterical watching me walk out. I have tried sitting beside the cot and it didnt work as he would cry and put his hands through the bars... each time I lay him down he sits up straight away. Even putting him down drowsy doesn't help🙄. We could keep going in to lay him back down for over 2 hours and instead of getting tired he gets over tired and gets more upset... hes in a grow bag and has a comforter teddy bear, Weve tried white noise and soft jazz music, weve tried dipping his soother in camomile syrup.. the only way to get him to sleep is to put him in to our bed and even at that it takes a while and he wants to be cuddled right into me. Once he falls asleep we put him in to the cot where he sleeps for most of the night and then wakes at 4 hysterical until hes put back into the bed where he will fall back asleep within a minute.

Any advice? Desperate 🙏