Brown spotting and cramping on day 17 of your menstrual cycle can have various causes, some of which may be related to fertility. It could be implantation bleeding, a sign that a fertilized egg has attached itself to the uterine lining. Alternatively, it could be breakthrough bleeding caused by hormonal fluctuations or an early sign of your upcoming period. Other potential causes include cervical irritation or infection. If you're actively trying to conceive, it's important to track your menstrual cycle and any changes in symptoms carefully. Consider consulting with a healthcare professional who can provide personalized advice based on your specific situation.