Hey, I'm A 21 Year Old Female And Have Had

Hey, I'm a 21 year old female and have had this lightheadeness feeling for the past 3 years. It's 24/7. It's gotten so bad that I've quit my job and I'm now at home. I got worse when I was about 6 months pregnant with my now 1 year old. In summer when it's humid out, my sinus kill me and the lightheadeness gets worse. They did a blood cortisol test 3 times and they all came back a very high number but were normal when doing a 24 hr urine test. Any ideas what it could be? Thank you