A pimple on your chin can be caused by various factors, including hormonal changes during both your menstrual cycle and pregnancy. However, it is important to note that a single pimple alone cannot definitively indicate whether you are experiencing your period or are pregnant. Other symptoms such as missed periods, breast tenderness, fatigue, and nausea are more reliable indicators of pregnancy. If you suspect you may be pregnant, it is best to take a home pregnancy test or consult with your healthcare provider for further evaluation.