That 1 week of antibiotics is not a very long course. Also, if they didn’t test your urine after the antibiotic was finished they can’t be sure they killed the infection completely.
Also, since 1 type of antibiotic does not all all kinds of bacteria, it’s possiable that the antibiotic you were on killed one type of bacteria you had but left others behind, that are now taking over and growing.
Maybe you should ask your doctor to culture your urine – that way they can identify the various types of bacterial colonies and choose an apporiate antibiotic for them all.
Keep seeing your doctor till the issue is resolved. Infections can cause scaring, and scaring can cause strictures. Good luck!