My 7month old boy does not fall asleep on his own

my boy is now 7months and was born 7 weeks early. He's generally a good night sleeper as he goes to sleep by 6pm and will sometimes wake up atnight for a feed still. I don't have any issues with him falling asleep for the night as I have stuck to a routine,bath, change into night suit,singing.

The issue I'm having is during day time, he's tired and moans to go to sleep but doesn't know how to fall asleep himself. I have to rock him for ages, bounce on the bed do whatever it takes for him to go to sleep. It's exhausting!  He is tired but just can't settle himself. If I leave him hoping he'll get tired and fall asleep himself he just constantly cries. I've tried putting him in the cot and using white noise, that didn't work. Any advice on what I can try for him to settle himself.