Losing weight

I never had a problem with weight up until about 1 1/2 years ago. I was always able to eat what I wanted and not gain weight. Even after having a child, I didn't have the usual problems, I lost the weight within a few months, no stretch marks, nothing! Then 30 started creeping up. It seemed out of nowhere I gained 13 pounds give or take. Where the heck did it come from and why won't it leave? I know a lot of people would probably want to slap me, especially if they have fifty to one hundred pounds to lose. But this has been haunting me, I have been the same weight since high school. I have dabbled in different diets from the lemonade to the Fat Smash diet by Dr. Ians. Granted I have lost between 6-8 pounds, but have gained it back with poor eating habits. It's so hard to change a lifetime of eating poorly. I have to prove a point to myself that I can do it. I have to have confidence and discipline if I ever want to succeed.