It is possible that you are experiencing a chemical pregnancy, which is an early miscarriage that occurs shortly after implantation. The faint positive line you saw on December 8 could have been due to the presence of hCG hormone in your urine at that time. However, as the days passed and hCG levels decreased, the subsequent test on December 16 showed a negative result. To confirm whether or not you are pregnant, it is recommended to consult with your healthcare provider for further testing and guidance. They may suggest repeating the pregnancy test or conducting blood tests to measure hCG levels accurately. Remember that home pregnancy tests can sometimes provide false-positive or false-negative results due to various factors such as improper usage or testing too early in the pregnancy. Seeking professional medical advice will help clarify your situation and provide appropriate guidance moving forward.