What do i do if i have suspicions that i'm pregnant and need to buy a test but can't tell my mum?

Call your doctor: Call your doctor or planned parenthood. You might even have a teen clinic at your school. Resources like these can help you by performing a pregnancy test, and helping you with resources - whether you want to carry the pregnancy, or abort it. Don't go this alone, though. Your resource people will help you strategize how to talk to your mother - if needed.