The HCG drops are well proven to be a scam, last I heard. The drops have been checked and they don't contain a thing in them, in fact I think there have been prosecutions for fraud or similar. The injections which some people manage to get off a doctor don't make any difference either, though. People lose weight because they're on a VLCD (very low calorie diet), not because of the magical properties of the drops. And 500 calories is very, very low. It's occasionally used medically, for instance as part of weight loss surgery, but that's the only time a VLCD is recommended. Both physically and psychologically, dropping to such a low level of calories will mess you up, and that's if you're healthy. We already have our bodies under enough strain without subjecting them to unnecessary drastic weight loss.
The 3 Fat Chicks forum is an excellent place to learn more about healthy weight loss and gain support while losing weight, including from other people with ME and especially with fibro. It has its occasional snags, I haven't seen a forum forum which doesn't, but overall I'd say it's a sound place, well-moderated and I learned a lot there. I've been losing at a nice safe speed of 1lb/week.
By the way, I reckon my former chaotic sleep pattern is a big factor in my putting on weight as well.