How can I lose weight when I have hypothyroidism?

I am a youngish person, and I am tired of weighing 200 pounds. I just reached that weight yesterday, and it is depressing. I wanted to know what kinds of exercise should I do that would be most effective, and what kind of diet plan would be best. None of the pills for hypothyroidism will work fo rme, so please do not suggest those. Thanks, and any help is greatly appriciated!