Thank you for posting.
Many things can impact a woman's cycle, (aside from pregnancy), such as stress, anxiety, weight changes, over-exercising, medications, illness, age, an infection, hormonal irregularities, or some change in lifestyle, etc.
We can't know the reason for your missed periods. Try not to worry. I would suggest seeing your GYN if nothing else to ease your mind. They will likely do another pregnancy test, even if yours have been negative. That's pretty standard in most GYN offices.