When I was 16 I was told I have IBS because of a pain similiar to yours. I discovered that right under my left breast, on my rib or maybe under, it`s really swollen and sometimes hurts. I had an xray done. It came back that I was alright. No tumors or anything. Not even buildup of gas. But I was always constipated.
Sounds like you DO have IBS and maybe losing some weight might help you out. Changing the way you eat, drinking a lot of water, eating fruits and veggies might help too. Even exercising.
There are pills for IBS that supposedly DO work. I don`t take anything for mine though. I had pain recently and went for another xray but the results said everything was still fine. I don`t think what you have is anything serious so that`s a good thing
Just try and take it easy and maybe try some of my suggestions. GOOD LUCK