I have flat feet and drop foot but my mum won't take me to the doctor, how can i make her take me?

If you are 18: You are free to go yourself. Try and explain to your mom that you are concerned with a problem you have and would like her to come with you. Maybe, there is another family member you ca talk too, grandparent? Aunt? Uncle? Father?

Go yourself: You are 18 years old and can seek medical care without your mother. Drop foot is not something to ignore, it may be a precursor to more serious neurologic problems.