Incomplete treatment comes to mind.
If you didn't finish your course of antibiotics, you could have grown some resistant bugs. Although not strictly an std
, it is possible that a sexual partner could have re-infected you if you had sex
during treatment. You might also consider using a probiotic
to replenish your natural vaginal flora and re-establish a proper ph. See your ob-gyn for more ideas.
Answer assisted by David Miller, Medical Student