I have heard that hormonal changes trigger body odor, as the poll in my blog also indicates that most people's odor tend to begin at puberty with the hormonal changes. You say that you're taking birth control pills, those are hormones. Did you notice if the odor got worse when you started on the pill?
Of course, bacteria does also produce odor, althought any microbiologist or medical doctor would tell you that jumping in some clean water and washing won't necessarily get rid of some bacteria. Your doctor can do a simple culture and sensitivity test to determine what bacteria it is and what medicine is required to kill it.