Today after working outside hard left side of chest hurts?

im 16 today i was working outside picking up heavy stuff shoveling, moving, raking doing alot of that and the left side of my chest started hurting... it hurts when i move and its hurting pretty bad right now.. idk what it is. its been doing it since around 2 or 3pm today. about an hour after i started doing stuff but i ignored it.. what is it. thanks.