He can be infected too, alot of diseases that affect women, show no symptoms in males. Go to your doctor and ask if your bacteria can be contagious.
Another thing that may be happening is that after unprotected sex, you may be wet for a long period of time, which is a catalyst for bacterias and yeast. Take a shower after sex or wipe, to reduce your risk. If that still doesn't work, try treating both the yeast infection and the BV at the same time.
Sometimes, it becomes a rather vicious cycle because the antibiotics kill too much of your natural probacteria (the bacteria that actually helps you) and then yeast begins to overgrow, and then you get a yeast infection.