Ultrasound to detect pregnancy?

Has anyone ever had an ultrasound to detect their pregnancy, when all other tests are negative? (Sorry if this is obvious, not sure how this all works)

I’ve taken three urine tests and a blood test at the doctors office - All negative. I have nausea and cramping, among other symptoms. Because of this, I’m being referred to do an ultrasound. I’m worried because I was told the blood test was going to be the real indicator of whether or not I’m pregnant (I was at 6 in hormone levels; apparently it is supposed to be exponential if I was pregnant).

Dates below for context:

Intercourse: 11/18 to 11/20

Period: 11/21 to 11/27

Onset of symptoms: 11/30