Bones under develop. Thinner day by day!

I am 18 year old bt my physical body is not well in my thinking.When i look other am feel jelous because of my thin and taller body structure.Please doctor suggest me what can i do.Am day by day worried about it.I never share my personal feeling to my family bt they think that m fit and fine bt am not. And next think my right side cheast rib is not similer and normal to my left side of cheast rib..I dont kno this is hapening from my childhood or not bt day by day on right side cheast are bone is pressed in inside. M very thin my my bone are not develop well..some time i think my bone are going thin day by day. stilk m 18 year old bt my height now good bt if it will increase its not fair for me sugest me plzz my health is fine bt i dont know why m going thinner day by day