A few months ago I was able to go without eating for days and overpower hunger-now I can't go one day. why?

It sounds like you're struggling to develop Anorexia. Unless you're a little person, 105 pounds is not a weight you should even consider starving yourself to lose weight at. I think the reason you can't go without eating for long is because you're already starving yourself and getting almost no fat into your body. To fast successfully (as in feeling okay and not passing out from low blood sugar), you need some fat and muscle on your body. That's what your body uses to make energy when there's no food coming in.