You're extremely honest with yourself, it seems. The answers to this - and your other post about 'wasting time' - are in your spirituality, I think. Very good advice about developing good eating habits and getting some exercise (not necessarily a great deal). That may help a lot with your physical self, which is very important. Also explore your spiritual self. Many highly intelligent people find their intellect getting in the way of their ability to believe. I suggest reading C.S Lewis "Mere Christianity".

In the end, whatever "screw-ups" you are feeling badly about are probably not very important in the grand scheme of things.... As put so well in another good book: "Don't sweat the small stuff. And it's all small stuff"