Hi.
Thanks for an elucidate history.
Gas,
constipation, anal itching are suggestive of an intestinal infection and might not have been caused by the antibiotics you are taking for
urinary tract infection.
I would advise you the following:
Get stool tests done on 3 consecutive days.
Other tests of blood and urine as needed including that for diabetes and
thyroid function tests.
Get a course of an antibiotic active against intestinal infection and yeast infection, anti-fungal tablet and
metronidazole. Take pre and probiotics, curds, banana and activated charcoal tablets along with PPI like
Omeprazole.
I hope this treatment will cure your intestinal problems.
Locally keep the area well washed with plain water and keep dry with hair dryer.
Apply liquid betadine twice day.
Have sitz bath if required.
I hope this answer helps you.