I have never once been able to make myself do anything through self-loathing and punishment. Self-regard and praise, on the other hand, are working wonders.
Get your nails done. While you're at it, pick up a new book or lipstick that you've had your eye on. Go for a walk in the sun and enjoy it the way you used to enjoy being outside in the fresh air as a kid.
My dear, life is far, far too short for all of us to waste too much of it being cruel to ourselves. We have no guarantees that anyone else in life will always be there for us, but we always have ourselves; treat that self well. She deserves it. And I'm not just talking about a mani/pedi here, I mean that you deserve--right now, right this minute, regardless of your weight--to be loved, to hear praise, to feel beautiful.
Give yourself that gift every day. Your own head should always feel like a safe refuge from the cold, cruel world.