Hi. Thanks for your query. Your history is very classical :: Pain in right side of the abdomen with back and increase in pain with sitting-up position. This usually occurs in cases of a typical condition where the muscle called ilio-psoas gets affected and has an abscess in it. YThe best way to get a diagnosis is a classical physical sign that a Surgeon can elicit easily. Get the diagnosis confirmed by CT scan of the whole abdomen and the lumbo-thoracic spine to see if there is an original problem inthe spine which has given rise to this sort of a problem. The treatment will necessarily depend upon the findings. If the psoas abscess is present , you will need an operation to clear the pus , get this subjected to examination. Tuberculosis is one of the commonest reason.