The past couple of nights ive been having problems with Kai at night. he would fall asleep for the…

The past couple of nights ive been having problems with Kai at night. he would fall asleep for the night pretty good.after he wakes up to feed for the first time,ill put him back in his bassinet but as soon as i lay him down he tosses and turns and will eventually start crying until i pick him.ive been laying him on his stomach,but since he has learned how to turn over from stomach to back,it makes it hard.i tried to lay him on his back,but he woke up within seconds..tried his side and he started crying.the other night i held him until i knew for a fact he was sleep,but by the time i got in bed,i couldnt go back to sleep.we use to co-sleep until he did the same thing.i tried him in his bassinet and i didnt have any problems.so he has been in there since he was maybe 2 months.the only way he'll sleep with me is if he's right under me on his side.if he turns over to his back,he'll wake up.if u put him on his stomach,he'll wake up....any advice? im so tired