My daughter was born May 18 so she is about 3 1/2 months old. She is really tiny unlike my other two kids who were always in the 90-95th percentile so I'm not sure if it's normal for her sternum to stick out this much? It's always protruded a bit but seems more pronounced as she has gotten a little bigger. Should I be concerned or do you think it can wait until her 4 month well child appt in a couple of weeks?