Does he has good neck control? Can he sit with or without support? It is best to take him to see a pediatrician for proper examination. However, don't over work/worry yourself, all is well by God's grace. I remember my nephew was misdiagnosed at birth to have down syndrome on the basis of low ear-set and low tone. Only for the boy to surprise every one some months later not showing any symptom relating to it and reaching his milestone approximately. Pls believe and pray