I know exactly what you mean. They usually want to wait until 18-20 weeks... those elective ultrasounds at 14+ weeks are magical for those of us that are impatient lol. I'd be happy to look at the image and help you guess.
Oh darn! For my son, by 12 weeks it was obvious as it stuck straight up and was sizable. I kept hoping it would flatten out LOL. By 16 weeks you would definitely notice a little something sticking right up.