If your last menstrual period was on July 31st and your recent pregnancy test came back negative, it is possible that you may have taken the test too early. It is recommended to wait at least one week after a missed period to take a pregnancy test for accurate results. However, since you are experiencing symptoms such as back pain, fever in the morning and afternoon, and continuous white discharge, it would be best to consult with a healthcare professional who can evaluate your symptoms further. They may recommend additional tests or examinations to determine the cause of your symptoms. Keep in mind that home pregnancy tests are not always 100% accurate, so if you continue to experience symptoms or have concerns about being pregnant, it is important to seek medical advice for further evaluation.