I Am Having Burning Lower Abdominal And Back Pain With

I am having burning lower abdominal and back pain with postprandial nausea and occasional vomiting. I also feel the need to move my bowels several after eating. I have had occasional fever and chills, lack of energy and general malaise. I am 1 month post op total knee which seems to be healing well. No notice of abdominal tenderness. No rebound tenderness from self exam.