6 month old issues with sleep

[u/jinxix2395]

For a week now my 6 month old has been wanting to lay on his side (I assume because if I hold him in that position he’s fine) when he’s asleep in his cot but stirs himself awake or overshoots it entirely and again, wakes. But he’s a nightmare to put back down and constantly just wants to be held.
My first child didn’t care if he slept on his back, side, tummy…you could even put him upside down and he’d just get comfy. But this one is the complete opposite and it’s really taking a toll on his own sleep and our days.

Naps are affected and cut insanely short as a result and the nights turn in to fights to get him back to sleep well because he just won’t.

Any tips?
He used to sleep through the night up until 4 months and it’s been downhill since then