I Did A Pelvic Scan A Day Ago And The

I did a pelvic scan a day ago and the result says Uterus: Normal sized anteverted uterus with homogeneous myometrium echo texture. No uterine myoma seen and there is excess fluid in the endometrial cavity.
Normal sized and stromal echoes. No cystic lesion seen adnexae is bilaterally free no fluid in POD, impression says pelvic inflammatory disease.
My question is what could be the cause, since I'm still a virgin and no penetration has ever happened before. Secondly I've been having irregular periods from onset and most times it comes in Black or brownish discharge colors it Also gives me severe lower abdominal pain, what is the cause of this too and can it be treated. Thirdly hope it's not a risk of future issues.