How is an ultrasound done for virgins?

I'm 16 years old, female. 168 cm, 75 kg. I haven't had any serious health issues before, I don't smoke, and I have no allergies. I haven't had sexual intercourse, but I have masturbated with my fingers quite often. Right now, I have a pulling pain in my right ovary and a feeling like there's something large there. My mom told me to get an ultrasound, and she says they will do it rectally. I'm really scared of that; I would prefer transvaginal or abdominal ultrasound. I'm terrified. I've never been to a gynecologist and I'm really scared of these procedures, and on top of that, I'm worried about my ovary.