Hello my son is 6 months old in 9 days and he has started laying on his face while sleeping is this safe? Im a first time mum so im really freaked out by it and i have to constantly roll him back, he can roll both ways and i always put him to sleep on his back with nothing in his cot and he uses a ergo sleeping bag so isn't swaddled please help as im really freaking out

Most babies will be rolling over by 4- 5 months. This is very normal as babies grow & become stronger.
Many babies then prefer to sleep on their tummy.
This is not something that needs to be stopped. It is important to make his new environment as safe as possible.

Ensure that the cot mattress is firm & flat & there is nothing soft or loose in his cot, especially as he is face planting at times.
You can try to turn his face if you see him with face down, but often, like rolling to tummy, babies will just go back to the position of comfort.
Always continue to place baby on back to sleep.
Increasing tummy time when awake may also helpful.
I assume his arms are free in the sleep bag you are using -  he needs his arms free.

Red Nose has the following information now that your baby is starting to roll.

Give baby extra tummy time to play when awake and supervised as this helps baby to develop stronger neck and upper body muscles which in turn enables them to roll back over.
Make sure that baby is on a firm and well-fitting mattress that is flat (not tilted or elevated).
Make sure that baby’s face and head remains uncovered (do not use lambswool, doonas, pillows, cot bumpers or soft toys)

As babies grow and develop they become very active and learn to roll around the cot.
At this time, continue to put them on the back at the start of sleep time, but let them find their own position of comfort.
By this stage it is not necessary to wake during the night to turn baby over to the back position

Do not use any devices designed to keep baby in a particular sleep position.
https://rednose.org.au/article/what-do-we-do-now-that-a-baby-has-started-to-roll-over