Hmm... first thing you do is make sure your heart is fine. Talk to your PCP about the pain, and see if he/she thinks it's necessary to look further.
One likely possibility is that it's spasticity or spasms of your intercostal muscles, similar to an MS hug.
This sounds to me like the MS HUG.
I am not yet diagnosed, but I get it with different type sensations i.e. right rib discomfort, sharp right rib pain, sharp right chest pain, and also the sensation where I cannot get my breath, like something sitting on my rib cage.
Also when I am walking for exercise sometimes I get to the point where I cannot catch my breath. Sometimes also after going to bed at night, I will notice that I cannot breathe in and out with a full inspiration/expiration.
I think many have different kinds of hugs. I think there is something in the Health Pages as well.
I hope you feel better......
I get that same pain, only on the right side. When I have it, it moves within a small area, but always in the same general spot. Fortunately it hasn't happened in a couple of months, as my ribs can get very sore indeed.
This isn't something I've ever mentioned to a doctor. I really don't know if it's MS-related at all.