What Causes Discomfort In The Shoulders?

for a few years, I have had shoulder discomfort, I used to lift weights and believe I hurt it benching heavy weight with bad spotter. sometime it feels like there is a ligament or something from my shoulder that runs down my tricept and deep in my shoulder blade/back that feels out of place, I don't know. I used to work out hard thinking it would get beter, but simply lifting my arm at 90 and pulling back is painful...any suggestions?