I'm freaked out

I'm 19, I struggle with PCOS and take metformin for it.

I didn't have my metformin from before Christmas, until yesterday.

I'm on day 42 of my cycle and my cycles usually last 30ish days.

I had sex, but we used protection for intercourse unless we were just messing around. He is positive he didn't cum inside me without a condom, but he came in me with the condom on and it was all in it. (This was between January 1st and the 14th. We only had full intercourse twice, but there was teasing a couple of different times without a condom)

I took a pregnancy test about 3 days ago and it was negative.

I have a transvaginal ultrasound on Friday.

Will they be able to tell me if I'm pregnant?

Should I try another pregnancy test?