Have you seen a doctor? Have you had a cold or the flu or any other symptoms like that in the past? I'd bring my body over to a qualified doc.
If you have not seen a doc, why not? All kinds of theories and guesses can be offered here, but the only logical thing to do to get a REAL answer is to see a doc. There's no one here that can give you any meaningful answers. Medical doctors are pretty good at these things. give them a try. Unless you want meaningless guesses that get you any closer to wellness.