Changing my diet

So, I have decided to change my eating habits just a little at a time. I tried once before and like many others, my old habits crept back in. The difference now is my kids need me to be more healthy. I'm a big soda drinker. I love my cherry Dr Pepper but I had to change a bit of my habits this summer. I was taking my daughter to church camp this summer. I didn't want to be the fat mom who couldn't keep up.My plan had been to exersize by walking before we went. Unfortunately I procrastinated, then the week before camp pulled a back muscle. So I went to camp the fat mom. I was disappointed in myself. I have overcome so many hardships in my life and im letting this bad habit of no exercise and bad eating beat me. While at camp I needed water, lots and lots of water. It was hotter than hell in Alabama this summer. So I started putting 1 oz of gatorade in 27 oz of water in my water bottle. I did this a few times a day. I had 1 Dr Pepper a day. So when I came home I decided to change my habits, a little at a time. My water intake is going great. Im logging on mfp now to add in my food, and a little exercise which will all inprove slowly. I'm very excited but im super tiered because I think my body was so used to getting its caffeine and now its punishing me. Has anyone else had a similar thing happen??