Why does my rib pop out when I'm on my belly?

My rib sort of pops out when I lay on my belly with my chin leaning on my elbows so my back is kind of arched. It doesn't hurt but it's uncomfortable and I have to either lie on my back, stand up or just wait for it to go back into place. Can anyone explain this?


You’re underweight


A doctor might be able to explain that, but we can't. We have no way to examine you even if we were qualified to do so.