possible miscarriage

Rachel
So I recently found out I'm expecting baby #2! We have been super excited. But today at 7 weeks I started bleeding. I am hoping it's nothing. But i also passed 4 blood clots with what looks like some tissue. So I went to the doctor and they took some blood to test and I'm supposed to come back in 48 hours to have my blood tested again to see if my pregnancy hormones are rising or falling. 
Has anyone been through this before? I'm just trying to hope for the best but prepare for the worst.