I was going to say the same as ZE. My metabolism is shot. Strangely I noticed it after I had the kids. I'm not obese but I'm much the same. I have to exercise a sh*t load and eat ridiculously low cals to lose. At one stage I worked out I couldn't consume over 700 cals a day with a one hour cadio work out if I wanted to lose 1kg a week.
Then right before I got pg with DS2 I found low carb high fat. I gorged on bacon and eggs cooked in butter. Omelettes..... and I dropped a dress size in a month with pretty much no exercise. All the other diets left me starving but I was always full. So I'm back on it.