Pelvic ultrasound Bc of irregular period

Ok so, my last period was in early June, I had interacted with someone in late May but my period came, plus it was mostly genital rubbing. Anyway I decided to take pregnancy tests in July and they came back negative. I was still nervous and scared so I went to pp and the results were negative. I decided to take another last week and it was negative. I decided to go to the doctor and he said I’d have to get a pelvic ultrasound but I’m honestly scared. Also I don’t eat a lot and I seem to be fluctuate between 180-200. When my period first started at 14 they’d tend to last for almost three weeks and now I’ll tend to miss them for two to three months at a time.. idk I’m so stressed