Advice PLEASE bleeding and cramping

Can anybody relate? I am 5 weeks 4 days today, went to ER today for worsening cramps and bleeding. My hcg doubled since Monday (went from 742 to 1539) I was seen two other times in the ER for spotting and cramps as well but less severe. The first hcg was 388, second hcg a day later was 622, third hcg 3 days later was only 742 and then the 4th was the 1539. My progesterone taken 4 days agi was only 4.4. The kicker is they don't see even a gestational sac on my ultrasound or anything in my ovaries or tubes. Could my body just be slow? Could it be to early yet? I'm so anxious and just want to know what's going on :( my bleeding is reddish Brown and my cramps feel more like period cramps now