my lower back hurts when I arch it but relief after a decent arch. Also my ribs tend to rub my anytime I try to build my core or slim down. my tailbone seems to be protruding further than normal. I cant sit up straight I either lean left, right, or forward resting my elbows on my thighs or knees. No tailbone pain but sit ups cause it to rub the skin and either irritate or tear it, it is not polyps it only happens with a repetitive sit up motion leaning left or rite prevents this, so I am stuck with crunches which is even worse on my lower back.