About 2 weeks ago I noticed inbetween my butt cheeks towards the top at the tail bone I did not have any muscle there. It is just skin over bone. It comes to a "V" shape and then my cheek muscle take over from there. Is this a problem? I know I am a little under weight but I have never noticed this before. It's like I am loosing muscle there. If I put on weight (which I'm trying to do) will this problem go away or is this is symptom for something much more serious. I have good healthcare but would prefer not to see a doctor at this time.