Last spring I had a what ended up being a benign ovarian tumor removed along with my ovary. It caused a lot of the same symptoms that you listed. Yes, it could be the cause of the "IBS" problems. I won't tell you that it is or isn't cancer, the only way that can be done is by surgery. My only advice is to make sure that you understand what the docs are telling you, hound them if you don't understand, and if something doesn't feel right then don't settle with what they tell you. I had one doctor tell me that there was nothing there, that the "cyst" had burst - this was after a laparoscopy - come to find out 6 mos later it was still there! If you havent' found it already, John's Hopkins has a wonderful Ovarian Cancer website. The ladies there are truly wonderful and informative. Good luck with everything!
I had a similar experience, only my "cyst" was much smaller 8x8x7cm, but the same fullness feeling, bladder pressure and IBS along with Proctitus. I had the cyst(Endometrioma, or Chocolate Cyst), Ovary,Fallopian tube and Endometriosis removed last week by a Gynocological Oncologist. Please reassure yourself that the MD you are going to has a specialty and you were sent to the GYN-ONC because of his/her expertise. Over qualified is better than under qualified in any medical case - justmy opinion! I am also in my 30's and the GYN-ONC told me that the incidence of being malignant at my age is slim (usually occurs in patients 50 or over). Saying this, I would think your age would also be a great factor. I hope you like the MD you are being referred to, I liked mine and knowing I was in good hands made all the difference in the world with nerves and anxiety. Good Luck to you!