What does it mean when the sonogram results say that there was no yolk detected in the cul de sac at 8 weeks?

The technician who performed the sonogram did an internal as well as external. The results also said that there was no heart beat that could be detected. Is there a possibility that maybe there was just a mistake on the technicians behalf. My Dr told me in my last prenatal visit that this could possibly mean I may have a miscarriage or that I am earlier in my pregnancy than I had thought I was. My fiance and I had every intention of conceiving and we based my fertility off of ovulation charts. The likelyhood of me becominh pregnant at a later date seems out of the question. I have not had any complications what so ever. I am still undergoing the symptoms of a pregnancy and have not experienced any pain, cramping, or l bleeding. What could this mean?