R.K.
Does he have some sort of musical stuffed animal like a glo worm, or a mobile that plays music? My little grandson, 14 months, will settle down almost immediently if I start singing 'Hush Little Baby'. My other grandson, almost 4, would stop figgiting in his sleep as soon as his glo worm started. The glo worm (now a seahorse) is motion and sound activated. So as soon as he gets restless it will play the music. The glo worm only costs about $10. I would get him one and when you put him to bed squeeze the glo worm and it will play, evertime he gets restless it will play. Hopefully it will let his brain know it's sleep time.
This could be teething--how many teeth does he have? Is this a new thing he is doing? Any new noises around the house inside or out?
Good luck Momma. Sleep deprivation is not fun.