Back pain connected with same side abdomen pain is mostly caused by kidney stones or urinary tract
inflammation. This pain is usually associated with more often urinating, burning when urinating.
Pain on left side of abdomen might be also caused by diverticulitis
of large intestine. This is associated with flatulence
what can explain left abdomen enlargement. If you suffer from constipation
, flatulences this might be diverticulitis.
It is necessary to perform blood tests and urine tests to find if there are any signs of inflammation.
Ultrasound of abdomen should be performed as well.
Hope this would help