Why bacterial vaginosis keeps on coming back every after my period?

this is the third month i had bacterial vaginosis. after my period i had this fishy smell that it is so disturbing. i have to wear a pad so not to scatter the smell on my pants. i always buy vaginal suppository. last time after several days i medicate myself, it coes back again. in a month i had it twice. then it will go, after period of next month, it will come back. i am not having sex with anyone. they say detect the root cause of bacterial vaginosis. i know i got this from my boyfriend few years back who i found out was having sex with different girls. now this is the root cause of my infection. how will i cure this without it coming back permanently? seems like any brands of vaginal suppository doesn't work anymore even flagyl. what will i do? the doctor seems could not treat me. they will check, give medications for relief but it comes back. it makes me depress. thank you.