Helmet for flat head?

My baby is 6 months old and he’s been having a flat head for a while. We addressed it at his 4 month check up and the dr said it’s fine and he will grow out of it. We noticed it more on one side vs the other. I’m starting to get worried. We obviously put him to sleep on his back but he rolls over and likes to sleep on his stomach. We basically try to keep him off his back but that doesn’t always happen some times. Did any ones baby need a helmet to shape their baby’s head? I kinda don’t like this doctor I’ll see what he says at his 6 month appointment. This dr kinda half ass the appointment and it seams it would be too much work to put in paper work for the helmet. His doctor even said he doesn’t really like to give them to baby’s idk what to do. I feel so bad because his head is really flat in the back. I have great insurance too. I feel like I should be given the option at least.