Did you DTD before hand? That can cause some bleeding.

I had a huge red 2 day long bleed at about 5 weeks the Dr I saw said I had miscarried. I went and got a scan and they couldn't see a HB and said to come back in 2 weeks for another one. I went back at 8 weeks when I had more bleeding and there he was perfectly happy floating around it was a bruise in the side of the uterus at the implantation site.

I had more bleeding at 18weeks and again at 28weeks, one was after DTD, one was out of nowhere, I got monitored and all was fine. Since then I haven't had another bleed and have a big fat healthy bubs waiting to come out! Try not to stress, I know it's hard but by the 3rd bleed I was very "meh" about it (boy who cried wolf sort of thing). They can be from subchorionic collections that are just bruises in the uterus wall from implantation and other things, they can get better, get worse or stay the same. Mine got worse, then healed itself. The nurse said it's like if you hit your knee on something you get a bruise under the skin but theres no skin in the uterus so it comes out esp if you DTD and it makes the uterus contract it pushes out any blood that's in there.

Fingers crossed it's nothing major and all turns out well, good luck at your scan!