Dizzy spells

Rose

So for a month now iv been lightheaded and dizzy. Getting worse over time . Like yesterday i was driving in the highway and i had to pull over due to feeling suuuper faint. Iv been dribking alot of water eating as best as i can. Im on active duty orders currently so im trying to work thru it. My doctor said that when i stand up my heart rate shoots up . Im not pregnant, im not dehydrated, im not sure whats going on 😕