As you may know by now, i'm 18, male, and a hard gainer. I always try and use good form, but haven't really been perfect until recently. Recently i've started noticing a slight pain in the front of my left shoulder. I don't know how to describe it - it feels more like a strain. It doesn't sting or anything its just a slight pain thats accented heavily during benchpress and and other chest/tri exercises that uses the shoulders as stablilzers and then accented even more heavily during shoulder exercises. Once i stop the exercise, the pain/strain feeling goes away immediately and only comes up again when i do shoulder/shoulder inclusive exercises. Do I have a rotater cuff injury? What's wrong with my shoulder? I would hate to have to give up gym time but but i'll do what i have to do to keep this from getting worse.

Of course, I might be over-reacting because the pain during exercises such as benchpress isn't too bad because i can still complete all four sets. I can also complete shoulder presses, but i had a harder time completeing side raises. Let me know what you think i should do.

Sounds like rotator cuff injury. Search the web for exercises that strength the rotator cuff. This is an area that takes a lot of stress when lifting heavy. I have injured both of mine and still have pain to this day. One from softball and the other from weight lifting. Hope it gets better and good luck.