Daily temperature rising to 99.5-99.9. fatigue, dizzy, fast pulse. all conditions disappear when i lay down. bp is fine. possible cause?

Backwards: I think you have the cart before the horse: fever causes volume depletion. All your symptoms (x the fever) are typical of volume contraction. The essential question here is: what is causing your daily, recurrent, low grade fever. This may be a challenging evaluation as the possibilities are exceedingly numerous. If this has been going on for a month, you will need an extensive workup.