I know what you are going through, because I have go through it my self. I even fall back on voiting as an attemptto make myself feel better - if (on the odd occasions) it does make me feel better its only for a few minutes, then the orginal problem comes back up.
The reason why you are too tired to fun these days is becasue your body isntgetting the fuel it needs.
In a bizare twist - under eating is going to do the oposite of what you want. your body stores fat for when it needs it (its from our hunter gather days)ie. times of low food, or cold weather, excersicemakes your body use that stored fat as energy.
When you eat less, your body goes "low food time - store everything you can"by eating less, you are telling your body, that there isnt enough food around, so it does its best to only use as little energy as possible (ie your too tired to run now) and triesto store every bit of extra energy in the body. this gets stored as fat.
please not im not a nutrotionist or a doctor - but that is how it was explained to me.
I think you are on your way to having a problem. if your not confitable talking to a doctor, go see a nutrotionist or a dietitian, as they can help you understand what your body does and doesnt need.
and on a side note - i lost weight when i stopped vomiting. I didnt to any extr exercise or eat any less - in fact i eat lots of snakes much of the day. Try this. you dont feel like your eating much but your body is getting the fuel it needs.