Hi.
Thanks for your query.
Noted the history and understood the concerns.
Diarrhea, changes bowel habits, pain in left lower abdomen is indicative of entero-colitis. Added
frequent urination can be due to irritation of a part of the
urinary tract or UTI.
This can be diagnosed by the following:
Get the tests of blood,stool and urine.
Clinical evaluation by your Doctor.
Get started with antispasmodic as you have pain.
Get a course of an antibiotic if there is any evidence of infection.
Continue taking plenty of oral fluids, multivitamins.
Since you have changed bowel habits during periods too, it would be better to go for an opinion of a Gynecologist and Gastroenterologist and get
colonoscopy,
ultrasonography or CT scan of the abdomen.