I would urge you to find out the details from your blood tests. Has your doctor been testing for free T3? If not then rather than hope that any outsider's words can have much of an effect on an individual with so many years of education and training who nonetheless failed to test for free T3, I'd find another doctor.
It's possible that you've been prescribed Synthroid, but not at a dose that gives you enough free T3 for your body to function well.
Unfortunately, as you've experienced, hormonal problems can cause a snowball effect where the balance point for the body becomes an overweight point, or even an escalating overweight point. In some cases, someone at your weight is factually eating considerably less than a lighter person, yet continues to gain.
If it's the case that your doctor hasn't been getting your free T3 level to a midnormal range, then I strongly, strongly urge you to find a doctor who will help you there.
Another thing I'd very strongly urge is that much dietary advice on fats is terribly wrong, saying that "polyunsaturated fats" are good for you . Some polyunsaturated fats are: the particular Omega-3 fats called DHA and EPA. The main polyunsaturated fat, though, found in most vegetable oils is quite bad for you, changing the composition of your own bodyfat in a way that's strongly associated with obesity and metabolic disorder. (An article on that will appear here soon, so you will have more detail in a bit.) You will not have a quick fix by banning soybean oil, safflower oil, sunflower oil, and corn oil and a few others from your diet, and really limiting chicken and pork fat, but over time the benefits will add up.
High fructose intake also, over time, can add to considerable metabolic damage. This would be an intake exceeding about 25 grams per day. This is found in only 200 calories worth of fruit. That amount is fine, but avoid more than this, or refined sugar (which is 50% glucose) and avoid significant high-fructose corn syrup intake.
Exercise is extremely important to addressing metabolic problems that exist in situations such as you are experiencing, but of course your breathing has to be taken into account.
I am not an expert on dieting methods or exercise for situations very similar to yours, and so am having to stay general rather than give a specific set of exact things to do.
We have seen some very remarkable things with Indigo-3G where previously-unreversible very overweight condition, including 100 lb overweight, had occurred. This is due to correction of underlying metabolic problem rathr than as a stimulant, which it is not. I would recommend it based on those results.