WARNING TMI- Probable Miscarriage

I tested positive end of February and would be a little over 6 weeks today. I started having brown/pink spotting a week ago. It last three days. I went to urgent care, had tons of blood tests ran and an ultrasound. Ultrasound showed a gestational sac but it was empty. Doctor said they measured me at 5W4D and it could be too soon. Told me my HCG levels were normal and to get blood work again three days later. Blood work showed my HCG increase to 4601 (nearly double) on Friday. Saturday night the spotting came back. Sunday I started having mild cramps and back pain and the bleeding progressed to a heavier flow. I only passed one clot but I’m not sure if it’s the sac or tissue. I’ve googled miscarriage tissue and nothing looks like what I passed. Still bleeding currently but no clots or tissue. I have an appt with my OB tomorrow and feel certain I will be told I’ve lost the baby but I wanted to get other opinions to prepare myself.