It could be flat head which tends to occur due to side preference. How old is he and does he tend to sleep or look to one side more than the other? GPs aren’t bothered about flat heads because they class it as a cosmetic thing more than anything else.
My LG has similar to this from sleeping on same side all the time, she got referred for physio but everyone has assured me it will round off as she grows and starts moving more. Can already see a difference now that she’s rolling and trying to sit up. She’s 5 months x
No advice but I’m here to say my little boys head is the same and I mentioned it at the jab appointment and the doctor said it’s normal because he’s sleeping on one side of his head so it’s flattened down but it should even it’s self out eventually as he starts sitting up and crawling and stuff x