You can opt the comfortable postures to control the pain and if that does not help then add some pain killers at safer doses sos but your priority must be to find a cause and fix it.
A pain in chest of that severity is intriguing with causes being as simple as a muscle strain
to as serious as a cancer. It may be a pleurisy
of some etiology.
I would advise you to have a skiagram chest-AP and Lateral and a USG chest if there is any fluid investigate it's sample.
If even then a doubt; go for a CECT CHEST and a Biopsy
if a lesion is found.
Key is trace the cause and correct is as soon as possible and not only pain management.