Hi Kkccoo,
I am in a similar situation right now. I went in for a pap (I'm 27, 2 adoptive children, no biological children of my own) and after the pelvic, ultra sound and transvaginal, confirmed I have a cantaloupe sized mass on/around my ovaries as well. Aside from being more tired than usual, and a little forgetful, I've had no side-effects of it as well. From what I've read, however, these things can creep so slowly that you don't even realize you are sick and/or changing. I can't wait to see the new me when this thing is out of me! Anyhow, that was just this passed Friday, and I had an MRI on monday, but haven't heard any results yet. So what I'm about to tell you doesn't come from experience, but from what little I've read throughout the weekend.
Any mass within you has potential to be cancer, which is typically why radiology and people from the cancer depts along with an ob/gyn/onc will take care of you throughout this procedure. Once they operate and remove the mass, they'll test it for cancer. An MRI and a C-125 blood test, should give a better look at what percentage it is that it is likely to be cancer. I am happy to tell you that a VERY small amount of cysts end up being cancerous, as most (over 90 percent from what I've read) are benign (non cancerous). You should wiki 'ovarian cysts' and it will tell you some good info to start with.
My dr said any cyst over 5cm can not be shrunk by medications, and will need surgery, so my guess is you will need it sometime in the near future. Depending on what your cyst is filled with and it's size, will depend on what kind of surgery you will go through. This area of information is definitely not something I'm well versed in, as I've never even had a single stitch in my life, much less gone through a surgery. This path is very new to me as well!
Good luck on your path! My suggestion would be to find a dr you are comfortable with, and don't be afraid to ask questions! I do not like dr's myself, personally. I wish I would have kept up on my paps (The last pap I had was about 6 years ago before this past friday) and perhaps it would have been caught earlier. I love my specialist, and even the people in the waiting room raved about him. I'm glad to have him on my team through this journey!
By the way. I am 37. No Children. I didn't feel anything. I was gaining weight.