I'm 25 and have low estrogen with recurring BV after sex. Is the low estrogen weakening my vaginal wall and causing bv?

Check partner. In your age range, it is not uncommon to be "re-innoculated" with bv, and some "prone" more than others. Anything that enters the vagina (tools, toys, self, or partners) can potentially bring BV (or other stds) with it/them. They should all be clean. This includes your partner(-s) who may need tested to be sure they are not accidentally giving you back what you keep getting rid of. Ask your gyn.