Do your mother and sister normally react like this when you fall ill? Because, if they frequently act like this then you need to sit them down and have a serious talk with them. Although, if they act like this whenever you fall ill, especially if it's as bad as you say it is, then they won't take ANYTHING you say seriously. You may want to bring this kind of thing up at school or some other form of authority that can stand in for you in this situation and, maybe, make them take your situation seriously in future. Cos this sounds like parental neglect to me. Unless, you've pulled stunts feigning illnesses in the past, then your mother has no excuse for her behaviour.

Go to the hospital, something could be seriously wrong. Bring a friend or, if you're a minor, a grownup you trust with you. Your mom won't be able to ignore the hospital bill they send her, at your request. I would advise to go no contact from her and your sister in the future.

Google your drs number and talk to them yourself? You are allowed to advocate for yourself, you know. If it's genuinely as bad as you say then call the Dr and if it turns out you are really ill then your parents can explain themselves to child services...