Welcome
Losing water the first week and not the second is a common pattern. Read Why the Scales Can Lie here http://forum.lowcarber.org/showthre...627#post8883627 to understand the initital process. Slow and steady weight loss should follow.

Suggest you read one of the Atkins books to understand the plan and how it works. If you don't have one yet, the rules are at the top of the Atkins forum here. http://forum.lowcarber.org/forumdisplay.php?f=98 Also read back for various threads in that forum for views on artifical sweeteners and also how to stop sugar cravings.

Throw out the raspberry ketones and make your own.

There is an entire sub-forum on thyroid here, read back on some threads about losing weight after thyroid removal. http://forum.lowcarber.org/forumdisplay.php?f=76

I am sorry that you are taking tamoxifen. I did as well, during a time I also ate mostly vegetarian, and the combo caused a 60 pound weight gain. There was a clinical trial during year four to determine who were "high responders".Luckily I was one, so the doctor decided I had most of the benefit from it as possible and let me stop it. Important to note though, I had started Low-Carb No Starch, No Sugar seven months before that, and had already lost significant weight and all Joint Pain had stopped by removing all grains and sugar, long before the weight loss would have mattered. So was it the Tamoxifen or the crappy high-carb, high grain, vegetarian diet? I'd say it was the diet, because as soon as I went LC, the joint pain lessened, life-long skin rashes disappeared, and so many other health benefits. I can't now in good conscious pin the nasty effects on Tamoxifen (though I did when I begged to stop the treatment). My suggestion would be to eat a completely clean version of Atkins, no grains, sugar, artifical sweeteners of any kind, processed seed oils, nor processed meats. Call it real food, primal or anti-cancer version of Atkins, but I believe the extra effort will be worth it for your health!
All the best,