your best bet is to be honest with your mum about wetting the bed. tell here its distubing your sleep and affecting your school work and that you spoke to the school nurse who recommends diapers to help you get a full nights sleep a big plus is it will save on washing the sheets try a cloth diaper and plastic pants they will work out cheaper i don,t know were u from but in england the doctor cam give you free diapers until u become dry