Pregnant with twins??

I miscarried last month at 4 weeks & 5 days. I was 6 weeks pregnant exactly Friday & asked to get my HCG levels drawn & they were 25,700 something. My doctor acted like that was pretty high, I got them done again today, I wasn't told the number, just that my dr wanted me to come in for an ultrasound tomorrow. Which normally she wouldn't even see you at all until 10 weeks. Were anyone else's levels that high at 6 weeks & had just one baby? I'm getting nervous. Also, this is my second pregnancy & I am absolutely huge. I am bigger than my sister is with her 3rd & she's a month ahead of me. I look 20 weeks pregnant.