“I need advice ”

Im 20 years old female, 52kg and I've had some chest pain for years coming back, at first i thought its normal because parents thought i was being dramatic but i never understood them not believing and never visited doctor. The pain that comes so often is when i either walk outside, stand too much straight, and its described as dull pain on my left side of chest, its firstly starts there then spreads to back same left position just behind. It becomes so dull that i start to sweat, i used to try straightening my back often when it comes but pain doesn't go till i sit for 15mins or rest. My parents used to twll that heart cant hurt but i feel it that way, i feel something squeezing that part of chest that's making me disturbed. When im out i have to usually squat just to feel slightly bit better because i feel like i would faint Knowing that beside pain i often have problem with hypoxia when standing up and i faint often and body starts spasming after preventing fainting. Side note that i dont have anxiety attacks and not using medications. Any advice would be good and what could it possibly be