Co-sleeping

My son is 4 months old. When he was a new born i almost never slept with him. One night over the last few weeks he was sick, and i let him sleep with me. Ever since then he refuses to sleep in his bed and if he does it won’t be more than an hour and he will scream until I pick him up and put him back in bed. Once i do that, he knocks right out within seconds. I love sleeping with my baby but i want to stop this habit before it gets to bad. Advice?😕