why do doctors do this

Melissa
Basically I went into the er for cramps and they did  a pt test Hcg test to check my level a ultra sound and Pap smear  they told me I was pregnant the my hcg level is 3500 for 5 weeks 5 days  the ultra sound showed a sac but no baby it was in the middle like where the baby supposed to be  they found out I had bacterial vaginosis which can be harmful for the baby so they put me on antibiotics they also gave me a A prescription to come back in tomorrow since it be two days then from when I came in the er  and just to see if my levels go up in my hcg  but on it it says possible misscarriage I'm so lost has anyone been through this I just wanna cry