Miscarriage ?? !

Went to the ER because I was having some bleeding. First time having bleeding. After they ran blood work they told me my HCG levels were too low for my estimated 10wks of pregnancy, they did an ultrasound and didn’t see anything so I was then seen by an ultrasound tech and did an abdomen and vaginal ultrasound where they also didn’t see anything but only a yolk sac which was estimated to be 6wks. According to my clinic I’m 12wks, I said 10wks according to intercourse, the ER said 6wks according to the yolk sac. They also told me it could be a miscarriage or a issue in fetus development so the growth stopped. They didn’t find a heart beat or see anything. What does this mean? Am I not pregnant? Did I have a miscarriage and not know? I’m stressing out.. they mentioned something about failed pregnancy??? I’m not sure what’s going on!