I've Been Having Chest Pains On My Left Side For

I've been having chest pains on my left side for 24 hours, I've taken different types of medicine for gas and heartburn and nothing seems to be working. It hurts when I get up really fast or if I try to lay on my left side. It's a piercing pain that also feels as if there's something squeezing my heart & it hurts to breathe, I have to slow my breathing down so that I won't be in pain. What could this possibly be from ?