peekay,
Sorry to hear your U/S wasn't fabulous. But you're totally right at least you know. The constant BD really takes it out of you doesn't it! Now you can relax a little. A shame the dermoid has grown. Is that going to change how things proceed?
Don't rule out O in the next few weeks. Keep checking the cm and try the OPKs. One of those little follies might decide to do the right thing. O could sneak up on you any time - don't miss it!
Good luck