I never worked out in my life and never had any motivation to do so. I am in a different situation, I have always been tiny, 100lbs but still very much out of shape. After I had my daughter I decided to work out to try to gain some weight. I never thought I would like it and now I do. It did not help me gain weight but I did gain muscle and feel better. If you are a SAHM like me going to the gym is a break. I go to the Y so I can take my daughter, she loves it so it has been great for her too. I have made friends, so it doesn't feel like a gym. If you have a YMCA close, they are cheaper, have childwatch and are much more like a community than a gym. I was one of those people who would laugh off any suggestion of working out, why would someone like me even need to work out.... everyone needs to do some sort of physical activity no matter what. I am also in school so for that one hour three times a week I do not have to think about school or chores. It is like a brain break. I have something else to concentrate on. I work out in the morning before I lose motivation. We get up get dressed and breakfast and then go. I am home before lunch, then my daughter takes a nap after lunch. She gets to play and gets her exercise too, and is worn out. The days I don't want to go I think of something I want, even just Starbucks, and say to myself if you want that then you have to do this. Think of a reward, and after going then you get it. I want a new comforter, I better go three times a week for a month. It is my reward to myself for doing something good for myself. Win win. It has become a routine and part of my schedule. If you can make it work one week why not keep going with it, so come up with a schedule that works for you and stick with it. If you miss one day or don't go you will throw the whole thing off.
So, find a gym that you are comfortable with, and one you can take your daughter to. The Y is great b/c they are more than a gym.
Come up with a reward system.
Make a schedule.
Find classes that you love. I love my step class, it is a huge challenge for me. I look forward to it the most and feel guilty when I miss a class. Weird for me.
Of course you have to stick with it. Which is the hardest for most people. I had a trainer the first year because I knew I needed to be accountable to someone. It helped me greatly to be motivated even when I didn't want to be. If you have to get a trainer for 6 weeks just to give you the start you need then do that.