Hello,
Thank you for your query at DoctorSpring.com
I understand your concern.
The symptoms that you intermittently experience are very classical for a gall stone or a kidney stone but that has already been ruled out. Please do not worry about cancer, as CT would have shown if there was any sign of malignancy. It is not IBD either, as IBD is associated with mucus and bleeding in the stool. Could be endometriosis, as you say it is related to your cycle, a transvaginal ultrasound can be done for a conclusive diagnosis.
Will you be able to share the CT reports if possible?
Feel free to discuss further.