DS is almost 24 weeks and has always been a tricky napper. Until about a month ago, he would only sleep on one of us or in the car. I managed to 'nap train' him so that he now has all his naps in his crib, but in the last couple of weeks he's started crying every time I put him down for a nap. He'll be tired and rubbing his eyes, but as soon as I put him down he cries. I have to lean in and hold him tight and eventually he'll pop his thumb in his mouth and go to sleep. But I feel the amount of time we're doing the crying/holding is actually increasing and it's so stressful for both of us. What can I do? I don't feed to sleep, and he's not too bad overnight so I don't understand why naps are always such a battle.