I have had the same in this preg. I lost my fist preg at 6 weeks so I was megga stressed when I bled in this one. I had old blood and a few bright red bleeds and I thought the worst too, but every time I did have a bleed I either went to my doc or the hospital and I always got a u/s - I did it for my peice of mind. It turned out I had a small tear in b/w my placenta and the wall that had a small bleed and the blood was coming out slowly. Eveything is AOK and im nearly 33 weeks!
Good luck I have my finger crossed for you!!
Kate