Hi, It's Dr. C. Board certified Ob-gyne. I can help you today.
I'm sorry that you're having this worry about your late period. The home pregnancy test will be accurate at about the time the next period is due and for sure by the time it's 1 week late. So it sounds to me you ran it not too soon.
If you skipped your period and aren't pregnant, there are a lot of other possible reasons. If it's just one skip, it could be stress. If you tend to skip, there are tests we can take to figure out the reason and treatment. Possible causes include eating disorders, thyroid disease, excessive exercise, too high levels of a hormone called prolactin, a condition called PCOS (polycystic ovarian syndrome) and a few others.
So if it's a single skip, it's fine to just watch for now. Most likely the period will be back to normal by next month. But if it's not, it's time to see a gynecologist who will take more history and run some tests.
Please reply if I can clarify anything or explain things better.