Is Gestational And Yolk Sac With No Fetal Pole, Heartbeat A Miscarriage?

I am 5 1/2 weeks pregnant. Having problems with lower back pain, they aren't bad and come and go. I have small white clots when I wipe after I void and some are in the toilet. I'm extremely exhausted and my HCG level are 21000, but when I went for an ultrasound all they saw was the gestational sac and yolk sac, no fetal pole or heartbeat. Does this sound like a miscarriage?