I'm Really Struggling With Eating And I Have A Really

I'm really struggling with eating and I have a really big control issue around it I have a voice in my head that keeps telling me that I'm fat and that I'm losing control everytime I'm eat. I'm also really struggling to get out of bed and do revision for school I just don't want to do anything at all and I want to spend the whole day in bed. Do you know why this is ? Also I'm 18 and female if that helps