The left side of my rib cage has been obviously protruding for 2 yrs now, what could be wrong?

Bone/'metab/lung. Comes to my mind diseases of the bone like osteoporosis or lack of vitamin d, or metabolic diseases that affect the bone. If you have a lung problem like copd, emphysema or chronic bronchitis or asthma the hyperinflation of the lungs could do it ( it's common to have pigeon's chest in COPD or asthma.).
Scoliosis? Scoliosis, or curvature of the spine can cause one side of your ribs to protrude.