Welcome to HealthcareMagic. This left sided pain if is present close to the pelvis then it can be due to kidney stones, pelvic infections, urine infections, twisted ovarian cyst
or rupture of ovarian cyst ( if you are a female) or irritable bowel syndrome
. An ultrasound and CT abdomen can be done. For the flatulence, upper GI endoscopy is helpful in confirming the diagnosis of acid reflux
disease or peptic ulcer disease
. A gastroenterologist should be consulted.
Hope it helps you. Regards.