I am bi-gender as well, though I lean more towards my female side and would have been born a cis-female if I could have chosen. Nonetheless, I am familiar with those switches. I can't say why it's happening to you or me, though you should
not be taking hormones unless they are prescribed or you are absolutely sure of what you are doing. To do so just to push yourself to one gender "side" decisively could be dangerous, and I don't know, at any rate, that hormones can actually convert someone from non-binary (like bi-gender) to binary. Speak to a gender therapist or endocrinologist for better advice as far as hormones go. A trained gender therapist or counsellor who deals with gender should have some experience, too, with non-binary identity, but you can always ask about this over the phone or in person when making a consultation.
As far as the science goes, there isn't much research to my knowledge out there on bi-gender/genderfluid individuals specifically. One scientific avenue you can explore is V. S. Ramachandran's relatively new categorisation of "alternating gender incongruity," which he uses to define bi-genderism, which he defines as a subcategory of ->-bleeped-<-. Whether or not that model is accurate I have no idea, but it's something to explore if you want to look at a scientific model. Ramachandran does a lot of work on split-brain patients and on "unusual" phenomena produced by the brain, like phantom limbs, and you can sort of see why he would be one of the first to explicitly theorise about bi-genderism.
This is the link:
http://www.ncbi.nlm.nih.gov/pubmed/22364652For me, I just honestly feel like there are two sides to my identity, two doors, so to speak, and when one is open the other is usually closed. I just let myself be. If I am wearing girls' clothes, makeup, etc. and feel a switch happen, I usually get the desire to change my clothes and remove the makeup, but it is not an overwhelming desire. I try to just let it pass, and usually it does. I'm not trying suppress my male side, but I do feel able to prevent that dysphoria to some degree by reminding myself, in the moments when a switch comes from female to male, how much of my life I've lost not having had a chance to express my inner girl.
Being bi-gender or gender-fluid can be difficult, but if it is who you are, it can also be a beautiful thing that differentiates you. You get to examine and experience gender in a way that not everyone does. And if you want to be female more than anything else, just be what you want, and see what happens from there. If your female side is so dominant, you should be able to live as the girl you contain/are for the most part. Your male side may not be as much of a problem as you think once you are happily presenting as the person you feel you are, and, ultimately, your male side is another piece of what makes up the puzzle of you. And if your therapist thinks it is a good idea, you can begin to transition as a gender-fluid individual, but this is a big choice that you must be certain about.
I'm not sure if any of that helps, but I hope it does. Good luck with everything! I'm sure things will work out eventually.

Gabby