I have a diet question?

I'm a 47 year old female, 5'3", 182 lbs. One day I woke up & said what the heck happened!! I used to be 125 lbs. I changed to a more physical job; 12 hour rotating shift where I walk a brisk walk most of it, stairs, and physical work the rest. I have muscles, but you can't see them because of the fat. I tried SlimFast, SlimQuick, Atkins, cleansing, but can't seem to stick to any of them. How can I get down to a good healthy weight? What's the difference between calories and calories from fat? How many calories from fat should be in a 1200 calorie diet? Does Weight Watchers point system work? Does Alli work? Sorry for all the questions, any help would be appreciated.