I'm sorry you're having to go through this - the worry is by far the worst part, isn't it? Hopefully after your surgery you'll have all the answers you need.
In the meantime, the best thing is to try to distract yourself. The worry and anxiety is really hard to avoid, but it can help to do things like lose yourself in a good book, or go for a run/do yoga/anything else active that will raise endorphins and help you feel less anxious.
If the pain you're experiencing is preventing you from doing anything aerobic, it could help to confide in any friends of yours who are good at listening. At a time like this, lots of well-meaning people will automatically say "don't worry - it's fine", which can feel like they're dismissing how you're feeling.
If you know anyone who will really listen to you and let you unload exactly how you're feeling and what you're worried about, it can make a huge positive difference. It might even make you feel better-prepared; people who can act as a sounding-board for you are a huge gift at a time like this.
I myself am being followed for an ovarian mass, so I know how stressful the waiting can be (as well as how easy it is to keep imagining the worst case scenario). As for myself, after my recent follow-up U/S, they want me to have an MRI - I'm currently waiting to hear back from the hospital as to when that'll be, so I'm currently following the same advice that I'm giving to you.
Anyway, I just wanted to say hi (and welcome to the board), and I'm sending good thoughts your way.