What Could A Mass In Lower Left Abdomen Be?

Hi I attended my GP 3 weeks ago as I felt something hard on my lower left abdomen which I haven't felt before, I am passing urine frequently and it is waking me up through the night, I am a 36 year old female with a history of endometriosis. I am waiting on an appt for ultrasound scan however in the last 3 weeks the mass has grown. What could this be? My GP carried out a ca125 test and my levels were higher than expected, should I go back to my GP before my scan