13 week old sleeps all the time, can't help but worry! Second baby

[WhyTheHeckMe]

Please don't see this as a brag as it definitely is anything but. My first ds never slept till he was 1 so having a baby that does is lovely but at what point should I worry?
He wakes at around 7am and will be awake for around 1 to 1.5 hours. He'll then sleep till around midday, wake for a bottle then sleep again till 4 or 5pm. Then awake for 1.5 hours ish before going down for the night at 6.30 or 7 and the he'll sleep till 7am.
When he's awake he is absolutely lovely - happy and smily and makes lots of squealy giggly noises so he doesn't seem to not be developing well.
I just think he seems to sleep so much. He has a pretty flat head at the back as he hates tummy time too.
My first ds was rolling over by 9 weeks as he was so well practiced due to no sleep, they're just so opposite. Not sure when it should be of concern that he's sleeping so much (awake for around 3-4 hours in a 24 hour period)
I've raised to hv and doc who both light-heartidly said to make the most of it (I definitely am).

[JiltedJohnsJulie]

If he’s having all of his feeds and is bright and alert at times, I wouldn’t worry. I’d be more concerned about the flat head.