I feel for you - have a very similar situation myself... some of the culprits that people suspect (not that they've all made it into mainstream science yet):

- medications you're taking (steroidal stuff and some antidepressant type things are notorious for interfering with weight)
- yeast problems (tons of threads on that here)
- food intolerances (grains, dairy, soy, etc. ... that's one reason why something like the 'meat fast' that's talked about on this forum might be helpful for some)
-thyroid (blood tests don't necessarily tell the whole story... can do a temperature test... see www.brodabarnes.org for more info, I'd get their free info packet... also www.thyroid.about.com)
- something else as-yet undiscovered**

** I think that's a HUGE category... does anyone have thoughts on what if anything is contributing to the weight problem in the U.S. and elsewhere - aside from the usual portion sizes and too-much-of-this-or-that and too-little-exercise argument? There seems to be a sizable contingent of people whose bodies just don't agree to lose weight despite their following accepted diets and 'doing all the right things' - I wonder if this was the case 100, 200 years ago??? Any social/historical statisticians around?