Baby sleep

My LO is turning 5 months in a few days. He used to sleep in the baby cot. His last milk for the day is usually 9-9.30pm and he is on full FM. Few weeks ago, he started to wake up every 30mins-1hr. So we decided to let him co sleep recently. Past few nights he started to toss and turn and fuss, sometimes he flips over to his tummy while still asleep. I had to turn him back. I am afraid it will affect the quality of his sleep or his breathing. Anyone experienced the same? Does it resolve?