Tight bra ??

So I'm 16 and currently a 34A size. I bought a new bra and after a day of wearing it I had severe chest pain. I found that the main strap was quite tight but didn't feel uncomfortable at the time.  I stopped wearing it and have worn much looser bras for a couple of days. But the pain seems to be getting worse, It feels as if my chest is tightening, it worsens when I take deep breaths in and I can't move or sit up properly because the pain is unbearable. I don't know if the tight bra is the reason for this but I need advice on how to help it or manage it. Thank you!!!