Eating problems , as many answers as possible , help please?!

I can't bring myself to eat over 400 calories for fear of gaining weight overnight. I weigh myself more than 3 times a day and if the numbers increase I get really upset. Even if I know it's water weight or food weight. If I eat something that I shouldn't or go over my limit of 400 I will purge to get rid of it. I hate it inside me , I can feel it turning to fat on me and clogging my arteries. I can't keep it in , I can't help calling myself horrible names untill I get rid of it.

Since I left college I have very little social contact and the isolation has caused me to become even more depressed. I've started cutting myself everytime I over eat to remind myself that it hurts mentally and physically. I've been contemplating suicide almost every day for a good few months. The only reason I haven't acted on these thoughts is because of my little sister and the guilt I feel about leaving a wave of destruction behind me even though I feel that nobody cares for me.

I don't know what I'm trying to say really but do I have a serious problem and how can I help myself?