I feel like a complete failure

How is it that women can get drunk one night and end up pregnant? How is it that the women who try to get pregnant are rewarded with negative after negative. I take my vitamins, I take pregnitude, I drink lots of water, I drink special tea...but for what? I don't get what I'm doing wrong. I've had a normal, regular period my whole life until I started trying. Wth is up with that?? I don't understand what's wrong with my body. I'm just 20 years old, shouldn't this be easy??