I don't have answers for all your questions, but if you reposted this in the
Live Journal community for VP you will probably get many more answers. more people look at it every day.
You can still get bacterial vaginosis and yeast infections without having sex. When you say you wash everything really well, do you mean you use soap inside your vagaina? or just on your vulva? If you are using the soap inside your vagina that could be the cause of your bacterial infection, vagina's don't really need soap, they are self cleaning so to speak. Using soap can actually unbalance your vagina's PH and 'cause more smells and in some cases BV or yeast infections. You could also just be very sensitive to soap in the area at all.
The smallest tampons are usually called Juniors or Lights. OB tampons are also pretty small, when i still used tampons the ones shaped like OB were my favorite.