I think i have bv and i used the hydrogen peroxide douche and it seemed like the odor instantly started afterwards. maybe it's cleansing itself?

No: Douches are just not a good idea. Period. As treatments they are ineffective and they tend to disrupt the natural vaginal bacterial population. This can cause BV rather than treat it. If you think you might have BV, see your doctor to confirm the diagnosis (or not) and get treated appropriately.

Douching bad for BV: Douching of any kind, with hydrogen peroxide or anything else, will not cure BV and actually makes BV worse or more likely to persist or come back. Don't do it! You need antibiotic treatment, usually with metronidazole. See a doctor.