What Causes Fever Along With Abdominal Distension And Palpitations?

Hello, my 2 &half baby has fever today, started last night. Also notice her belly is big and upon palpation, i noticed that her tight side below the ribs is tender than the left side.Did not complain of any pain and still is active even with the fever. The veins are also visible on the abdomen. Im getting anxious, i dont know if this is jusg a normal process of some toddlers with a pit belly. Please help.