Well, just from my own experience, and also, from other people, heads can be quite bumpy, especially with a vaginal birth. Many people never feel there head, until perhaps they just happen to. Then they are amazed to find how irregular their skull is.
If you truly think this is new, then this is a very unusual finding, something that normally never happens, and it would be important to see your physician to see if anything shows up on cat scan or MRI (although routine blood work will likely be first).
I remember hearing a discusion on this topic before, and that this is basically impossible (I can't remember the source), unless in infection of the bone or trauma.
I did find one case where a deterioration of the skull occurred, but this was with a man who had an aneurysm, had bone removed from his skull for surgery, the bone flap was then replaced, and he got a staph. infection in the bone, which caused some destruction of the bone. You can see the x-ray results here: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2588247
The other thing, would be if you had had a severe injury, but if you had trauma to the skull like this, there would be damage to the jelly-like brain underneath the skull from the impact, and the movement back and forth from side to side that this causes - the brain is thrown against the skull and continues to "wobble" back and forth until it settles - much like jelly. And you would know you had been hit, or you would be in the hospital if you had.
So if you believe this is loss of skull, then please see your health care provider so that an examination can be done.
If you do not mind, I would like to know the outcome, and you are welcome to write back to this post (there will not be other charges for you to write back. and the post will stay open for awhile even after an accept is given if it is)
Let me know if you have any questions or comments.