Confused, 2 weeks earlier than thought?

Toni
Ok so my lmp was oct 5th. I found out I am pregnant November 18th. The test said 2-3 weeks. According to glow And lmp i should be about 9 weeks. I went to ER last night BC of migrane and nausea. They said I'm about 7 weeks. How is this possible? Could ER Be wrong?  
EDIT: I was pregnant with twins and miscarried one and that's why it was saying I was further along. I ovulated late.