I tried losing weight many, many times. My nurse that diagnosed my PCOS suggested the low gi diet (glycemic index). There is research done on how different foods effect your blood sugar levels. My examples off diet foods that actually made me fatter, right off the top of my head...Cheerios, rice cakes, popcorn. I don't eat it but watermelon is really bad too. So it might just be that the things you are eating within your WW limits don't work for your body. Hmmm. Here's a website that explains it...
http://www.glycemicindex.com/
I know it's frustrating but don't give up. Just find the things that will work for you. I lost 40 pounds on the diet, not really a diet, more like a new way of eating. I got pregnant and I'm still down 30 pounds after having the baby!
Good luck to you!
Becky