Back/Posture Issue

IF SOMEONE can solve this one..you will be a hero.

I am 41 now but have had this issue as long as I can remember. It i VERY odd, VERY real and has plagued me my entire life. It is so odd that I can hardly explain it to DRs who typically offer a quick incorrect diagnosis or some not needed test. My hope posting here is that  someone could at least give a recommendation regarding what type of provider would be best to look at this.

Symptoms - I listed this under back because that is the best guess I can come up with. The issue only arises when I am sitting down. When I sit down, my posture appears to be so off that (the best way I can describe it), my abdomen (gut if I  had one) pushes out and my hips roll fwd all the way. At this point the curve in the lower part of my back goes away. My hips turn so much that as an example, if I had change in my pockets they would empty out (sounds odd to explain it this way but dont really know any other way). The problem is that my stomach pushes so hard against my pants that is is VERY uncomfortable to sit down. Not Nerve pain....more of a discomfort that you pants are way to tight. This was so bad, that i sort of self diagnosed that I had tummy tuck surgery to get rid of any fat around my waist. I thought this would cure the issue, but it made it worse.  The surgery left me with very sore abdominal muscles that now hurt when I sit down. This is not any type of hernia, or Nerve issue. It is some sort of structure with my spine abdominal muscle. One other odd issue is that if I lay flat on my back, my ribs spread out some much, that it becomes uncomfortable..(as if there is no muscle support holding them together). I am pretty in shape (run 4-6 miles several times a week, weight about 190, 6' tall). Can anyone think of what the heck this could be...or what type of doc i need to go to. I need a doc that would do x rays of me in a seated position and then have knowledge to compare to what is normal.  I had a 40 physical recently and the doc mentioned briefly I had a touch of scoliosis. Also one doc noticed a small chip in a vertebra but couldnt tell anything. I would travel to any specialist who would listen and had knowledge to solve this issue. Thanks for any feedback and feel free to ask questions..

[grannienannie]

try to take a bone density test that all i can think of.