thanks for posting on HCM,
From your description it is very possible that you are having a kidney diseases (infection or stones) which will require to be confirmed by a doctor. Urine analysis (if possible culture and sensitivity test performed), abdominal ultrasound (specifically look at the kidneys), blood test
(CBC, urea, creatinine
, BUN etc) will be needed in order to confirm the kidney diseases or exclude it. If that be the case, you will require another course of antibiotics, take antispasmodic drugs, drink much water and consult a urologist
Other possible causes might be from the GIT such as diverticulitis
(like you rightly said and being on antibiotics does not mean you receive specific antibiotics for diverticulitis), severe abdominal colic due to intestinal infection ( i suggest stool exams + colonoscopy
to be done).
If pains are severe, I suggest you consult immediately or go to the ER.
Hope this helps