What's causing this to happen?

Hey everyone, so I'm 15 years old. My period usually comes around the same time every month since I started having them when I turned 13, but it hasn't happened since April 6th. I talked about this with my psychiatrist at IOP and she suggested that my mom take me to see a pediatrician.

So, I went there that week, and they did a pregnancy test for me even though I've never had any kind of sexual activity ever-I'm still a virgin, which is super important to remember. The test came back negative. They also took some lab work for me the next day, which all checked out fine.

Then two days later, I felt this sharp pain near my left ovary-it was like something sharp was stabbing me. My mom rushed me to the ER where they ran more tests, gave me some medicine for the pain, and did yet another pregnancy test that was also negative. They hooked me up to fluids so I could get an ultrasound, which showed nothing unusual-no ovarian torsion, no tumor, no mass, no sign of a baby or anything out of the ordinary.

They sent me home with instructions to go back if it still hasn't come by early August. It's now almost July and my period is still missing. I wasn't really stressed even though April and May were tough months-I was in the hospitla during that time, but it didn't seem like stress was causing this.