If there is history of fall or your rib is structed against some hard objects then fracture
of a rib is possible as your pain is of that type.
But as this is not in your case but you lift wt of 50 lbs it is more likely that you might have muscle catch and there is spasm of muscles giving rise to severe pain
You take some analgesics with muscle relaxant
tablet and you will be alright.
If you do not get relief then consult orthopedic surgeon.