I Have Had A Total Hystesectany, Bowel Screening 6 Months

I have had a total hystesectany, bowel screening 6 months ago (no polyps) and negative pap smear. I do have a mass the size of an orange laying on top of the vangina and a CEA test result of 5.9. and negative results on all other blood marker test. I have been told by two doctors they have no idea whats causing the mass and say the only way they will know is for me to have surgery. I am 75 years old. Do you have any idea what causing the mass before I have to have surgery?