Help on information about a shoulder/collar bone area

[Wiley87]

Right, so I've had this ****ing injury for years now, and it's not going away. It never used to be this bad, but now it's got to a point where I can't work out my shoulder period. Press ups don't go too well, and if I do too many the injury comes back twice as bad. I'll try and give you as much information as I can:

The pain is situated on my shoulder, but feels as though it's actually on my collar bone (only left side)
I can't put my arm behind my back all the way without feeling a little discomfort. It's small, but I can notice something isn't right.
It's only on my left side. I've never been weight lifting stupid weights, and I've never overtrained. I'm still pretty skinny, so I know what weights are too high for me.
You can't see anything different when comparing my shoulders, and sometimes the pain is barely there, but it will always have a little soreness.

I know you guys aren't doctors, I'm just curious if anyone else has had this problem. Thanks in advance.
Wiley