Sounds like your intercostals. Try foam rolling your sides starting at your lat and going down to your waist. Definitely mobilize your thoracic spine and work on lateral flexion. My upper back and sides are extremely tight and I have plenty of tender spots on my sides.

http://www.mobilitywod.com/2011/08/episode-299-improving-lateral-flexion-of-your-flank-bits/

http://www.mobilitywod.com/2012/07/clear-the-t-spine-now-we-can-start-talking-shoulders/

http://www.mobilitywod.com/2012/02/mwod-serratusrib-cage-mash-party/

http://www.mobilitywod.com/2012/11/the-500th-video-great-sub-scap-shoulder-smash-drill/