Heeeelp. My mum just overheard me

being sick. ages ago she suspected i had an eating disorder and after i ended up in hospital (for my ED and a suicide attempt but thats besides the point) i had to go to an ED clinic where they have since said i have sympotms like those of anorexia but because the assessment was recent i have to have more tests for them to diagnose me or something. no one knows that i make mself sick after eating and my mum thinks my eating habbits are 'normal' again and that everything is fine. i just came out of the bathroom and she said 'have you got an upset stomach'? i said 'i don't feel very well' which i think may have worked for now but what happens the next time she may guess i have thrown up. what can i say to throw her off the scent. i can't have an upset stomach forever.
please give me some advice. i know i am a headcase so no need to clarify that for me but i have nobody else to ask