K.W.
Hi there -
Don't be freaked out. My daughter who is now 16months had the same symptoms last year, when she was 4 months. And yes, she was born with a perfectly round head, she just wanted to turn her her to the side while she was sleeping, and she developed a big flat spot on her head's right side. She was diagnosed with Plagiocephaly. She was fitted for a Starband helmet and started wearing it before she was 5 months. She wore it for about 2 months 23 hours a day, then only for sleeping, then only for the nighttime until she was about 11 months. We ABSOLUTELY did the right thing by doing the helmet. She didn't even notice it when it was on, and now she's developmentally on or above her age, and has a nicely shaped head! My biggest advice to you is if you are going to use a helmet DO IT NOW! If you wait, your baby will have to wear it for a much longer period of time, since the skull starts to firm up. It seems like a huge inconvenience, but I hardly remember her having it now!
Good Luck -