Prior MFP member, trying it again!

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A couple of years ago, I decided I had had enough with my weight and decided to make a change. I downloaded MyFitnessPal, bought a Fitbit and jumped right in to my weight loss challenge. I met my step goal every day, exercised, logged all my food, drank my water and lost over 30 pounds. I made myself and meeting my goals the priority. Then somewhere over the last year, I lost that motivation. I gained 20 pounds back and am really struggling to find the motivation I had before. I feel it on Sunday, do my meal planning, go buy the groceries, get on my treadmill and then by mid-week, I am grabbing a sandwich because I didn't pack my lunch, drinking a soda to get me through the day and coming home and being lazy instead of working out. I start out tracking my food, but if I eat bad, I feel bad about myself and just quit. I don't know what is wrong with me, but I really want to get myself back in order. I have never really been involved in the communities before, but I am hoping it will help me get motivated again! Thank you!