Two and a half years is a long plateau, but maybe if you view this weight stagnation as a plateau you may find ways of busting it.
The body is an amazing thing. To prevent us all from starving to death in hard times it learns very quickly to adjust. If you cycle for 20 minutes per day after a while the body finds ways of doing it more efficiently so you no longer lose weight doing it. If you feed your body 1200 calories per day it soon adjusts its metabolism so you don't lose weight doing it. You need to shake your body up a bit. Do something completely different that it's not used to in order to make it start losing weight again.
The best source I've found for beating plateaus is SparkPeople. It helped me through a plateau at the start of the year. It turned out I was eating too few calories and my body went into starvation mode. If you go below 1200 calories per day it will slow your metabolism to the slowest rate possible to stop you from starving to death. Irritating, yes, but useful back in neolithic times I'm sure! I ended up increasing my calorie intake and introducing weights to my exercise routine and it shook me out of my rut. One of the tips some people here gave me was the idea of calorie cycling. So that your body doesn't adjust to your calorie intake make sure that you don't eat the same number of calories per day. Have at least one day per week where you eat more calories to give your metabolism a jump start.
(Article on calorie cycling: http://findarticles.com/p/articles/mi_m ... i_83343022
The other thing to consider is portion control. A few years ago I couldn't understand why I'd gained so much weight. I ate a very healthy diet, with few sweets and almost no junk food. I walked everywhere. Turns out it was my portions to blame. Even with the healthiest food imaginable if you're piling your plate up then going back for seconds you will find that weight hard to shift! This may not be your problem, especially as you've already tried Weight Watchers and that's one of the first things they teach you, but I thought it would be worth mentioning just in case.
You've been doing all the right things, but all the right things in the same way for far too long from the sounds of things. You may need to make a dramatic change to make your body start losing weight again.
Here is the link to the SparkPeople articles that helped me ( http://www.sparkpeople.com/community/as ... ts.asp?q=8
). I hope they help you too! Good luck and let us know how you get on.