Why want bacterial vaginosis go AWAY?

I have tried the pill flagyl, several times it semi works but makes me sick and tired and is linked to cancer in rats. I have tried metronidazole vaginal gel...it sucks! its messy and never gets rid of anything it actually gives me a yeast infection instead. Why want this mess go away? my doctor put me on the gel for the next 6 months but its ridiculous, ive been using the same medicine on and off for years, so why would it work now?? its not and it wont it will temporarily go away then it comes right back. is this curable or not? i throw away my panties everytime... wearing stupid pantyliners everyday.... and on top of that my sex life sucks due to the fact i never know what kind of discharge i will have,( thick or thin/milky white or clear) frustrating i'm only 21, no std,(ive been tested) and ive had the same bf since i was 16... anybody with some insight?? same problem? know the cure?