toddler sleeping

ashleyangelo20

My son is 18 months old and he usually naps form 12 to 2 everyday. Recentely he will sit in his crib and cry or make noises and play. i make it a point that he stills stays in there for those two hours so he has some sense of schedule. At night he goes to bed at 8. I hold him, rub his back and rock him. When he falls asleep he tightens up and will not let me lay him down in his crib. He screams and most of the time throws up.  How can I get my son to sleep.