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There must be ongoing bowel inflammation
which is causing the pain in the left side. You need to rule out Pancreatitis
because such condition pain radiates to the back as well. Does the pain increase when you lie back and relieve when you bend forward. Do you consume alcohol. Regarding the feeling of gas in the abdomen, you must try eating bland food for a while. It must not be very hot. Drink milk which will help in relief. You must see your Doctor and ask for an Ultrasound
to look for any damage to Pancreas
and get other required tests done as necessary. Kindly keep me posted.