If you are sexually active, then it might be a good idea to consider whether or not you could be pregnant. After conception, there are many physiological changes that can occur in the woman's body, including changes to the vaginal mucus. This, together with the fact that you are a week late for your period, would suggest to me that ruling out pregnancy is important. You could start with a urine pregnancy test, but you may want to back it up with a blood pregnancy test, which can be ordered by your regular doctor
If the pregnancy test is positive, of course you will want to visit your primary care doctor
to discuss your options. Similarly, if the test is negative, you will also want to visit your doctor to investigate other potential causes of mucus discharge, which could include a condition called bacterial vaginosis - caused by an imbalance in the normal bacteria living in the vagina - or a sexually transmitted infection. Your doctor will be able to perform an examination and determine whether you need testing or treatment for any of these conditions.
Please call for an appointment today, and good luck!