transvaginal ultrasound!

Cheyenne
So I went for my first appointment with an LVN just taking blood and paper work. She schedule me for a ultrasound on July 6th to see how far along I am because my dates confuse us both! 
Last period: April 25-27
10 negative HPT
Suspected next period: may 25th
4 positive pregnancy test at 18 days late of AF (6-12)
Has this happened to anyone else? 
How far along does everyone think I am?
I could be anywhere from 7 weeks-3 weeks!