Sorry about the double (now triple) post. I don't know what happened. I got an error, so I tried posting again.
Anyway, I just remembered something I read on /fit/ a long time ago that cracked the whole thing for me. If you eat too little, you'll have trouble losing weight (and you will even gain) just as much as if you ate too much.
Your basal calories is basically your weight in lb * 10. Eat that minus 100, and adjust as your weight decreases, and you will lose weight sustainably. Also exercise so that you don't completely destroy your muscle mass in the process. It's basically magic. You don't need to think about it. Just adjust your calories, rigorously count them, and do *any* kind of exercise while you're doing so.