I am a 15 yo with a sunken soft spot on my head

So for a while now (as long as I can remember) I’ve noticed a rather large dent/crater near the back of my skull. Kinda on the top. I never actually thought about it until I realised most fake human skeletons ive seen don’t have it, my friends don’t have it, and pictures of skulls don’t either.

If I press on it, it doesn’t hurt but sometimes theres a weird, sickening feeling but only on a scale of 2 from ten. It’s hard like the rest of my skull, not soft.

I’m just curious as to why I’d still have it if I had it when I was a baby. I’ve had no head trauma that I know of. But I’m curious if it could be the reason my memory is so bad.

Does anyone have this/know of this? Should I be worried?