You have a protruded occiput.
Most skull sutures do not fuse until 60s, and some never fuse at all. Sleep on your back, and make sure you do not roll onto your side in the night. Could you try this and tell me later if it helped? Take before/after measurements if possible. Ideally, no pressure should ever be put on the sides of the skull while doing this, and I'm guessing it would take months/years.
Also, how wide is your zygomatic arch. Google search images if you don't know what I mean. I'm particularly interested in the ends of the zygomatic arch, which connect to the sides of the neurocranium. I have a theory that underdevelopment of the palate as a baby will result in a narrowing of the zygos and thus the entire cranial base.
Cranial base shape has a large influence on protrusion of the occipital section, and that is largely genetic.