Hey mommas!

I need some advice- I’ve continued this one and only bad habit- my almost 18 month old gets rocked to sleep for his nap during the day. He’s been falling asleep on his own at night time and sleeps through the night since 7mos. I’m not sure what the problem is for day time nap that he won’t fall asleep on his own. I’ve left him in his crib and he won’t budge so I’ve been just rocking him so he gets a nap. I’m currently 21 weeks pregnant and rocking him is not gonna happen much longer due to my growing belly. I’ve tried again to just leave him in there but he’s not having it. Idk what else to do. Any advice would be appreciated!