Am I the only one this has happened to?

I'm 19. I'm 5 weeks 6 days pregnant and started experiencing period like cramps yesterday and brown spotting. Today, I started bleeding. I got in an emergency visit today w/ my obgyn. At first he said it was a complete miscarriage then he did an ultrasound and said he found more than he expected. The yolk sac actually grew which wasn't there in my first ultrasound. He then said it could be a normal pregnancy but he was calling it a threatened miscarriage and that all the blood could just be from the wall. I asked him if he had seen woman w/ this much blood and still have a normal pregnancy. He said yes and more blood actually. BUt he's also seen it the other way. I just got up from nap and passed a blood clot almost the size of a small golf ball. Not having severe cramps. Has this happened to anyone? If so, what was the outcome