LO cries himself to sleep :(

sam&tm

DS is not the best napper during the day- he just cannot fall asleep unless we're in the car or taking a walk in his stroller (which I think he's staying awake more now too).  He cries himself to sleep....anyone else LO's do this?  It's heart wrenching to watch him screaming because he's tired and just wants to sleep but can't.  On the other hand he's a great sleeper at night.