How do they usually do an ultrasound if you are a virgin?

I’m 18. Never been sexually active but I’ve done some fingering on myself pretty often. Lately I’ve had this dull ache in my right ovary area and it kind of feels like something’s bigger than it should be. Mom wants me to get an ultrasound and says they’ll do it through the back. I’m really freaked out by that idea. I’d rather do the belly one or the vaginal one . I’ve never seen a gynecologist before and I’m super nervous about the whole thing, plus I’m worried something might actually be wrong with my ovary.