My first HCG level was 36 at almost 4 weeks. Gestational sac present in U/S but no yolk sac. Is this normal?

I went to confirm my pregnancy and the walk in doctor told me that he doesn't think my pregnancy is viable (because my first blood test showed a HCG level of 36). He told me I will definitely miscarry or that I'm having an ectopic pregnancy. He sent me for a l ultrasound and the results showed that there was a gestational sac present but no yolk sac. At the time I was 4 weeks pregnant. My second blood test (2 days later) showed that my HCG level is 106. The walk-in doctor told me not to get my hopes up that this is unlikely viable. Can you see the yolk sac on a 4 week ultrasound? This doctor has convinced me that I will not continue this pregnancy. This is my first pregnancy. I'm going into my fifth week and have done nothing by worry! I always thought my first pregnancy would be filled with joy and anticipation. Instead I'm scared out of my mind.