Skin picking and eating... Is this normal?

Okay, so for as long as I can remember, I have been picking off and eating the skin around my fingernails, feet, toes, and scalp. And also I bite and eat my fingernails and toenails. I have bad dandruff patches in various places on my scalp caused by an excess of yeast building on my scalp and in parts of my ears, and I've tried treatments, but subconsciously I almost don't want them to work because I want to pick at and eat the skin. I remember sitting in class and scratching the flakes off of my head and watching them fall onto my desk. When no one was looking, I'd scoop up the flakes and eat them. This sounds really weird now that I'm typing it. But even now, I find myself scratching and looking for flake patches. Sometimes I don't even realize I'm doing it. Sometimes I even scratch until little scabby sores develop and then I pick at those. Recently, I tried this foot soak to get rid of the dead skin so I wouldn't be tempted to eat the skin, because I'm trying to break the habit. But the soak just made them peel even more and every time I'm alone, I start eating the skin. I haven't really been diagnosed with anything except PTSD when I was 8 (I'm 18 now) and I haven't seen a shrink since I was 12. But during the last few weeks before high school graduation, I was stressed and I think I had a couple panic attacks (I haven't ever had one before, but I started hyperventilating and couldn't stand up or move.) After that, I bit off all my nails and picked at my calluses on my feet. I feel embarrassed to tell my parents about this, mainly because I don't want them to think I'm gross or have a mental issue. I don't think it's bad for my health, but I'm just curious as to why I do this. I don't remember learning it from anyone, I just started doing it.