I posted a little earlier today about my experience when I was in my 20s - I could get by on very little food too. And I got so thin - 115 at one point - people were asking me if I was sick. Trouble is, it's not sustainable and I ended up gaining back every ounce I had lost and then some. Over and over again until I got *old*
and would actually gain weight on what you are eating now (no bull). I know right now *old* seems like it will never happen - but it will, and you will still care whether you are fat or not. You could try getting just a few more calories now and increasing gradually until things level out?