Shoulder Pain

Today my shoulder started hurting while carrying around a schoolbag. the pain wasnt too bad, then i lifted. now my shoulder is killing me.
The pain is right wherer ther front delt and chest come together. it is in just one area, like someone is stabing me.

ANy ideas on what it is, anyone else expirience it??

Could be some type of shoulder strain. I’d go easy training shoulders and back for a week or so, to let it recover some. If it’s still this painful and bothersome after that, it’s probably worth having a professional take a look at it. Also, when you have to carry the backpack, I’d use both straps to distribute the weight more evenly, rather than down onto one shoulder.