I recommend that you speak with your doctor
about your question. The most obvious explanation for many people who have not had a normal menstrual cycle is the explanation that they could be pregnant. If you have already taken a pregnancy test in the recent past, and this was negative, then there are many other possible answers as well. The female menstrual cycle is regulated by a number of different hormones that work to regulate each other through complex feedback and inhibition loops. If there are any changes to any of these loops, the cycle can lose its normal regulation and the timing can be off. Again, one of the most common causes is pregnancy, and so that should be checked first if you are concerned about a missed period. Beyond that, stress, weight change (either loss or gain), lack of sleep, and other medical conditions can all play a role. It would be important for you at this point to be checked by your doctor to make sure that there is no other concerning reason for your lack of a menstrual cycle for an extended period of time. He or she will likely repeat a pregnancy test, and then may do some other blood tests as well as a physical exam. Again, please speak with your doctor.