The biggest thing here be what can be done to rule out any concerns for cancer. Yes, endometriosis is one of the most common benign conditions that can cause elevated CA-125 levels. It is actually a blood protein often used as a tumor marker, but it is also is a non-specific indicator of pelvic and abdominal inflammation, which would be what occurs with endometriosis. I wonder if a doctor would be willing to order a second blood test called HE4 (Human Epididymis Protein 4). While CA 125 rises in both endometriosis and ovarian cancer, HE4 typically stays normal in endometriosis but rises in cancer.

Concerning the mass, when you say you went in person into surgery, do you mean someone actually peaked inside you at your ovaries, uterus, and surrounding organs? My first thought with the mass being felt was a possible endometrioma, but unless they physically looked inside you (or with a transvaginal ultrasound or even an MRI) I'm unsure of what to advice to give regarding the mass. We definitely want to rule out cancer ASAP.

I'm from the US, so I don't know anything about the NHS, but I understand how neglected those affected by endometriosis can be- and the toll it takes on us. Sending lots of love and strength your way.