Dear friend, welcome to HCM,
it looks like blunt trauma
unless you are dizzy/ breathless, it may not be serious. try simple analgesics like paracetamol
.5 to 1 gm 3 times a day or an ocassional NSAID
. local pain killer liniments can be applied .
if not settling, pl get an Xray chest done to look for fractures
take care and pl. keep me posted on the progress.