Sounds like an eating disorder to me - generally resorting to unhealthy and unhelpful methods like making yourself vomit are signs of an eating disorder. The problem isn't with how much you weigh it's to do with your perception of what you way which is messed up. Speak to a counsellor or doctor to actually fix the problem once and for all. Or, alternatively, if you want to put yourself and your loved ones through hell then just ignore it and let it get worse.