Church, boy scouts, moving due to a military father... That's kind of sad. ._.
Anyway, yeah, if I were you, I would really do everything I can to initiate transition as soon as possible. Writing a diary and such might help you psychologically, but that will in no way stop the physical harm that's being done to you by your own body.
If really, your parents won't understand, you can just act independently from them and worry about them understanding later. They don't sound like would react really badly anyway.
For example, you could:
-Find an excuse for an appointment with a doctor and go in alone (you have the right to), and then ask the doctor about this. If needed, you can simply find a random illness and its symptoms and say you're worried about a few of those symptoms.
-The same could be done to see a therapist. For an effective cover, the best would be to find one who has experience with trans issues, but doesn't exactly specialise in them. And no crap like politically/religiously engaged therapists with questionable qualifications. A real licensed psychologist or other professional.
-Find a trans-friendly, informed consent, etc. clinic and go there alone for help. I believe those truly understand and have expertise in helping trans people in difficult situations. They could probably prescribe you hormone blockers or real HRT, depending on your age, after just a quick process. Some also offer other support services like therapists.
If you see a therapist, for example, even if it's just so they understand (because the way I understand it, they have no say on the matter), as, for example, a psychologist with a diploma, that person will be able to explain your parents. After having seen the therapist for a while, you could call your parents in for a four-person appointment where the therapist (or even doctor actually) could make your parents understand that gender identity disorder is a true health issue, that it's not your fault, nor Satan's, and that it's been proven to require physical treatment.
A lot of very stubborn people will resist and explain things the way they want to, but will calm down and understand when someone highly credible explains. It's not a guarantee, but an expert's explanation very well might be all they need to finally recognise the facts.