Talk to General Physician on Dizziness, Fainting And Low B.P.

Assalam alaikum, I am 24 years old female with a BMI of 17.04, almost 11 years ki age se garmiyon me blackout hona start hua, school assembly lambi hojaye to body thandi parna shuru hoti thi which resulted into blackout and fainting, a school teacher said it was due to my brain not getting enough oxygen. Abhi bhi garmiyon me kitchen me kaam karte hue same feeling hoti hai to rest karti hoon but phir poora din boht weakness rehti hai, mera B.P. naturally 100/80 se low rehta hai. Please tell the diagnosis and suggest what to do. P.S. I think I have a fast metabolism.