Light bleeding and spotting during pregnancy can have various causes, some of which are normal while others may require medical attention. In the 17th week of pregnancy, common causes include implantation bleeding, cervical changes, or vaginal infections. However, it is important to consult with your healthcare provider to rule out any serious complications such as miscarriage or placenta problems. They will be able to provide a proper diagnosis and guide you on the necessary steps to take for your specific situation.