Hi and welcome to HCm.
Infection is caused by bacteria just as every other infection occurs. Considering you medical history and medicines there is a higher risk of vaginal and pelvic infections so this isnt something uncommon. More important than the cause is its treatment. Just continue with antibiotics and the do the swab test to check this out. If you have signs of vaginal blleding or spotting this is just a sign of arimidex
therapy and this shouldnt concern you. Wish you good health.