Antibiotics dont know the difference between good bacteria and bad bacteria, so they just kill it all. Thats why it is common to get thrush after antibiotics.

I wonder if a dose of strong probiotics could have helped? You cant take them with antibiotics as they will just kill them too, perhaps you could ask the doctor if it would be okay to go on a super dose of probiotics (check out fast tract on the main site, there is a forum banner for it) and that might be an answer for you.