there is some risk in long distance and self diagnosis so go and see a medical pro,
chiropractor or osteopath would also be my choice.
you may have 'stressed' a muscle, very painful but it should heal by itsself just takes a little while.
if there is a misalignment of the spine or ribs then a chiro adjustment is the right way.
if you want you may try a self help exercise for the upper spine as featured in my website: http://www.dorn-method.com
painkillers a ok as long as you can stop taking them soon.
i would appreciate if you keep me updated about your healing and diagnosis