Hello,
You're far too light, and aren't eating enough. The fact that your periods have stopped should cause alarm bells to this effect.
You should slowly increase your calories until you're eating several hundred more than you are at the moment, because sub 1,000 isn't healthy for anybody.
There is a lot of information on the fitness forum about how to eat a healthy diet and have a healthy regime; there's no need to starve yourself to extreme weights to achieve your goals.
I'm fairly sure your belly won't be "fat" at the weight you're at. Females often carry a little fat around the tummy, but it's completely normal, and you'll see that most people have it.
Hope that helps a little.