Alice,
As someone who repressed what I can see now from memory my true gender was I can truly commiserate with you. When I finally realized it I felt like my whole self-definition was lost - that my self-identity was a complete fraud, even to myself. It is a horrible feeling.
Over the past 11 months I have had to rebuild my idea of who and what I am. A difficult proposition because my discovery turns out to be that I'm something that the majority of people don't understand and disapprove of, the first of whom was my wife. It will be a tough road for you, I think, before you can be reasonably certain.
That said, though, I must add that it will be very valuable for you to go through this. If you think guidance would help, by all means speak to your therapist about it. He/she can point out things that maybe you haven't realized or given enough emotional weight to and "point your eyes" at the relevant facts that you may be too involved to recognize. One of the most effective techniques for me has been to imagine how I would feel and what I would do if there were no constraints, social, familial or otherwise, to keep me from doing it. This has taught me the difference between how I really feel and what I think I'm "supposed" to feel.
Good luck with this, hon'. I feel for you and wish you the best.
helen