The only way to physically change your body to that extent would be through surgery and hormone therapy. About the best thing that magic might help you do is become more comfortable of who you already are, and maybe gain an understanding of why you feel the way you do. I might recommend past-life exploration and meditation, if you ascribe to those sorts of theories and beliefs.
I have heard of it helping others who feel out of place in their bodies by developing information that the feelings come from having developed a habit of living many lifetimes in a particular gender, rather than swaying back and forth. So they develop deeper habits of thought and action more geared towards one side or the other of the spectrum. So when trying to break that habit/comfort zone, the result is a life spent feeling out of place because things just don't match up, without any real information as to why or how.
It is just a theory anyways. If other causes are ruled out or don't make sense, it might be worth exploring in case it might bring some comfort or insight.