no heartbeat

hi all, i really need advise here. went for my scan which doc at kkh counted as 6weeks 3days but turn out my scan only shows yolk size with a waterbag but there is yet to have heartbeat of my baby. i am so worried as doc ask me to come back for another scan in 2weeks time. Doc says my baby may be small or my ovalution is too early. what does that mean?