Do doctors check for plagiocephaly during well baby visits? How to revert a flat spot at 9 weeks without a helmet?

Yes. Your pediatrician should be checking for plagiocephaly at every well visit. The head is still very pliable at 9 weeks. It is important to rotate positions while the baby is lying down and also in the car seat. Plenty of tummy time, when you are awake will also help. Most cases do resolve on their own without the use of helmets.