Can tampons cause bv? I just got rid of it and then I got my period a day later and now I have BV again! I have never had this problem before.

BV. I don't think tampons cause bv. It seems that BV is an overgrowth of the bad bacteria in the vagina. It usually means your good bacteria is low. The good bacteria make peroxide that keeps the vaginal pH low and this inhibits bv. It seems BV likes to recur. My theory is that this is because you have not got the good bacteria growing well in the vagina. I would treat again and take probiotics.
BV. When the tampon is inside there is a stasis of the blood inside your vaginal which can lead to overgrowth of bacterias, hence bv. The more natural way is wearing pads and allowing menstrual blood to flow freely.