Hi and welcome to the forum! I am glad that I can help you.
You want to know the cause of the symptoms that you experience.
Sometimes, if women experience sexually transmitted disease or extra uterine pregnancy, the anatomical part called the cavum Douglasi can be filled with pus collection (abscess) or may contain remains of fetal tissue. Also, an abscess around the anus can be presented with pain in the pelvis.
According to the data that you described, you may or may not experience any of the medical conditions listed above. See a gynecologist to exclude any abcess in the cavum Douglasi.
Please keep in mind that I provide medical information only. I am not able to diagnose medical conditions online. Please contact your doctor for further advice and information about diagnosis and treatment options.