Because early pregnancy symptoms can also be indicative of a variety of other conditions, it's hard to say for sure why you're experiencing these symptoms.
The first thing you should do since your period is a week late now is to take a home pregnancy test. At this point, it should be pretty accurate. If it comes back positive, call you general doctor or OB right away and let them know so they can tell you what steps to take.
If the test comes back negative and you continue to experience these symptoms, you should call your doctor to troubleshoot the cause which could be anything from a winter virus to treatable conditions like insomnia or a thyroid condition.