My Daughter Just Pointed Out On FaceTime That Our Little

My daughter just pointed out on FaceTime that our little one was beginning to have a flat spot in back of head he will be three months next week. Next appt in in Dec should we be concern or start some treatment this grandma is a nurse and concerned .. She holds him a lot tummy time and attempts to turn in bed. He is a long sleeper at night 6 hours! Please advise