See an orhthopod 1st.
Does the pain bother you when sleeping, does it cause you to awake, does it bother you throughout the day?
How is your flexibility?
Do you warm up/heat it before exercising, ice it afterwards, take an
anti-inflammatory...without seeing-treating you, your orthopod will give you the right diagnosis, but I know you don't want to skip workouts...Try training chest-shoulders-biceps the same day, turn the muscles on and shut them down for rest for 5 days afterwards...warm up very good, do pec-shoulder-bicep stretches 3x for a honest 30 second hold. Work with machines in a pain free range of motion, use lighter weights and higher reps 15-20 to force fresh blood into the area for repair.
The shoulder is the most mobile muscle in the body...joint separation does not come from muscle mass. However, some people with a lot of muscle hypertrophy lack flexability and do not stretch nearly enough. Usually training heavy with sloppy form, ignoring a pain such as tendinitis and keep training with pain and week tendons/ligaments will cause some separation.