See your own doctor first, but if he/she can't pinpoint a cause, you might wan to ask for a referral to an infectious diseases specialist. My mom had recurring fevers and they found a small cyst behind her heart. They said it "grows" and periodically bursts, releasing the toxins into her system that would make her feel really lousy for a week and run a low-grade fever for a week or so, then the body would clean itself out and she'd be fine until the next time it happened. It's not life-threatening and can be treated with antibiotics, but requires more powerful antibiotics over a longer period of time (6-8 weeks) than your more common infections. You may not anything even totally related to this, but an infectious disease specialist is trained to look for the "out of the ordinary" things if your blood panels come back normal.