I keep felling like i'm about to faint, but i don't know why.Help!!?

I'm 17 , I've only fainted once in my life(when i was in a sports competition..and i put too much pressure on myself) but for the past 6 months,whenever i feel im in an awkward situation i start to feel strange,and its like im blacking out or something like that and feels soooo weird, i dont understand why this keeps happening..and i feel like im just about to faint, but it never happens