Came here to say the same as Harriet! My LG is under treatment from an osteopath for the same thing
My boy is the same wondering what to do!
My little one did this at 5 weeks, got him into see a chiropractor who massaged his stiffness away and he has been happily looking in both directions now.
I had the same worry but started putting things on the other side of her and encouraging turning the other way and it seems to have reduced as she's gotten older. I asked the GP about it at her 8 week check and she brushed it off. Then again, all the other local mums said they hate that GP and she's not very good 🤣
As with the other comments, we saw a baby osteopath who helped with tightness on my boys right side neck, helped him move more freely definitely.
My boy did this from 2 weeks till 10 weeks and now he looks in both directions x
He might have some tightness in his neck - maybe look into seeing an osteopath?