Pregnant with twins??

I miscarried last month at 4 weeks. 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 and was told they're going up good but was not told the number, just that my doctor wants me to come in for an ultrasound tomorrow. Normally she wouldn't even see you until 10 weeks. Were anyone else's levels this high at 6 weeks & just had one? I'm getting nervous. This is my second baby & I am absolutely huge. My sister is pregnant with her 3rd & a month ahead of me & I am bigger than she is. I look 20 weeks pregnant.