Hello, my 3 year old has a fever once a month since she was 1.5 years old. She has had 2 bladder infections and the last time she got tested for one, it came out positive for a bladder infection, then negative when we wanted to double check. Now she has a fever again one month later, and had been complaining of sore legs, stomach pains this morning, and also back pain . What could this be??? It just keeps coming back almost exactly once a month!