Going on to have a healthy pregnancy after a scary start.

Hi all, I'm hoping someone can relate to what I'm going through and perhaps have some positive outcomes. I had some light spotting last thurs and was booked in to go for a scan. Going by my LMP and positive test, I should have been 12 weeks. At the scan they couldn't see anything so had to have an internal. She then asked if my dates could be wrong as she was only seeing a yolk sac and put me around 5.5/6 weeks. Was told the pregnancy probably stopped developing and my body hadn't registered it yet. Was told to come back next week (today) for another scan. I started to have bright red blood when wiping and a few clots. (For the last 5 days) alongside cramps and lower back ache. I went for my scan this morning and fully expected them to say I'd lost it. They were able to pick up on the external but asked to do another internal. Baby has grown and theres now a fetal pole and yolk sac, but they are concerned that the growth isn't as much as they would expect for a week. No heartbeat because she said it's still too early. I now have to go back next week for another scan, but they advised that I may miscarry during this time. Has anyone been through anything similar?? Has anyone had any positive outcomes? My head is a mess, I just wanna know whats going on.