Discomfort ribs/left side below ribs

I had my surgery about 7 years ago and haven't had any problems until this last year.  Anytime I am in a seated position I have severe discomfort (not pain) below the left side of my rib cage.  It feels like there is something pressing on my stomach from the inside out.  No pain, just feels strange and uncomfortable.  It goes away if I stand, and only have it rarely when I lay down.  Any ideas or has anyone heard of this?  Thanks!