Thanks for posting your query.
From the description, it seems you might have developed shoulder muscle tear.
There might be possibility of tear in your shoulder muscle because of overly or abruptly stretched shoulder muscle during heavy weight lifting.
I suggest you to consult an orthopaedician nearby for a detailed examination. You may get the X-ray/MRI
of the area affected under his/her guidance.
Meanwhile I advice you -
To give rest to your shoulder and arm.
Stop doing weight lifting for some time.
You can take nonsteroidal anti-inflammatory drugs (NSAIDs) to reduce inflammation and pain under supervision of your treating doctor.
Wishing you speedy recovery.
Dr Sauarbh Gupta