What Causes Bruise Like Pain In Left Ribcage Area?

I am a 30 yr old white female. 5'7" about 185 lbs. I was stretching to my right side and I noticed a bruise-like pain coming from my left ribcage area. I felt it with my fingers and there is a narrow firm thing under my skin that feels like a hardened vein or something. It's about 3 or 4 inches long. Looking in the mirror I can actually see it pop out when I bend to the right and stretch out my left side. It is also bluish in color. It isn't extremely painful but it is tender when I press on it or stretch it out. Is this something serious?