New to FitnessPal

Hi, my name is Sheri and I am (as the title states) new to myfitnesspal. I downloaded the app to my phone on a whim, then spent the last hour or so browsing through some before and after pics, and I'm really really hoping that I can make this work for me. I am a 32 y/o stay at home mom. My starting weight is 245lbs, I am 5'11". My goal weight is around 155lbs. My activity levels are pretty awful, my life has turned very sedentary. As a result my knees are hurting me all the time, my back is always hurting, so my main reason for trying this (beyond just losing weight) is I want to feel better in my body. I have been overweight since I had my first daughter in 2003. I gained like 80 lbs while I was pregnant. My daughter passed away shortly after birth, and I had no desire at all to exercise or watch what I was eating, I was too depressed. Sooo, long story short, I gained more weight. Then I lost some weight. Then I gained it all back and then some. When I got pregnant with my second daughter in 2008, same story (happier ending) I gained like 80 lbs. Then I lost it all doing the Atkins diet. Then I slowly gained it all back, and now here I am. I found the before and after pics very inspirational, so I am starting my diet and fitness journey today! Cross your fingers for me!