Worried about DD's head

I think she is getting a flat spot, I don't know how/why as I only seem to have noticed in the last month or so, and she doesn't spend anywhere near as much time lying on her back as when she was only a newborn.

it's in a bit of a funny spot though, on the back of her head but more towards the top, I didn't think that would be the spot that would be lying flat on a surface. She really doesn't spend much time on her back at all, except on her change table when changing her nappy, when she is asleep but she does roll around a fair bit and probably spends half the time on her side or tummy. The only other thing I can think of is the time she spends lying on the floor, as we have timber floors but if I put her down on her back it's on a rug (which has another rug/blanket underneath so its not quite so hard), and she usually rolls over onto her tummy straight away anyway. Would the hard floors (even though she isn't lying on them that much) be causing it?

I felt her head this morning when I got her up and there was almost an indent in it, must say it freaked me out a bit :o But after a little while it was alright and just felt a bit flat.
Should I go see my MCN about it? Or will it sort itself out over time. She has a lot of hair so its not visually noticeable, only if you run your hand over her head.