What Causes Gradual Decrease In HCG Levels During Pregnancy?

Hi I am 24 years old, and this is my first pregnancy. My hcg levels were at 34,000 when the doctors said i was miscarrying, 30 hrs later it went up to 36,000 a week later it dropped 13,000. i still feel my body preparing for the baby can i still be pregnant? i was at 7 weeks and there was no heart beat, could it have been too early? I dont feel that i lost my baby.

Thank you