You need to see a doctor for tests. It can be so many things. We cannot diagnose you over the internet.
i had this problem for awhile now
How long have you had this problem? You could have anything from an infection, to severe hormone loss, iron deficiency, or hypoglycemia. Have you seen a doctor yet for these symptoms?
Be sure you're well hydrated, and not salt deficient. If this continues, get to a doctor for some tests.
Take care,
Enzy