Can't help you with the birth control, but regarding the bone loss I would strongly recommend you look into transdermal natural progesterone supplementation, after checking out the works by Dr. John Lee, as well as his website.
Long story short, Depo contains synthetic progesterone, which will either block your body producing natural progesterone or take up the receptor sites for the natural progesterone. Progesterone is critical to bone building and Dr. Lee is one the few physicians who's ever waved a flag about this point. I seem to recall a study he published on his website about increasing bone density in geriatrics through supplementing with natural progesterone.
I could go on about calcium too, the thing about minerals is that they only work in concert with other minerals ... if you don't have the right balance in your body you screw up your chemistry worse than if never supplemented at all. Nancy Appleton, Ph.D. has produced some facinating books that revolve around nutrition and minerals. Essentially, if you read any of her books you learn that calcium deficiency is NOT due to a lack of calcium in the Western diet, we're actually consuming more calcium than ever before. HOWEVER, calcium cannot function properly without the proper amount of phosphorus to facilitate it's functioning. She wrote a book entitled "Healthy Bones, what you should know about osteoporosis" that you should REALLY look into.
The works of these physicians goes against conventional medicine, but it's your body and your bones. I say go for education and be willing to think outside the box. If they say things that you totally disagree with, fine, but if that is combined with valuable information, you don't throw the good out with the bad (which is what conventional medicine just LOVES to do). But let's face it, if doctors knew it all your bones would be as strong as ever.