Or am I not explaining things clearly enough? I thought I was, but...

So here's the story. I'm 22, female, and as of today's appointment apparently 273 pounds. Yeah. I've always been big, but the last several years it's been getting ridiculous. In high school I was a steady size 12/14 -- not obese, but def. overweight, but I was comfortable and more importantly I was active so at least I was a semi-healthy kind of overweight. Since being put on Zoloft in 2001, though, my weight has steadily ballooned until I'm now a size 20. Here's the kicker, though: I eat less and actually exercise more than I did when I was in high school, and yet the weight keeps piling on.

I know part of this is due to age and slowing metabolism, as well as genes (pretty much my entire family is big), but I decided to do a little experiment over the summer. I cut out 90% of the worst foods I was eating, exercised more often and more rigorously than ever, *and* took a low-dose water pill every day. And what happened? I actually GAINED weight.

Every time I bring this up to my doctor he gives me the spiel about getting older and metabolism slowing down and etc, but to me it feels like there's definitely something more at play here. To tell the truth, I don't eat much. I usually eat two or three moderate meals a day and that's it. I drink water like a fish. And yet...

Is it possible my thyroid's messed up? I had some blood work done over the summer and supposedly everything came back okay, even though according to one of those self-diagnostic tests online I've got too many symptoms of hypothyroidism for it to be pure coincidence. Could it be water retention? My legs swell up something awful due to water, to the point I can actually leave dents in them because it's built up so much, but again, my doctor blows me off and says I'm just not trying hard enough to lose weight.

So what's the verdict? Should I seek out another doctor's opinion or just suck it up and accept that I'm doomed to keep getting bigger without cause?