Help! What could cause my menstrual period to stop?

hello! I'm 21 years old. My menstrual period has been delayed for a month and few weeks now. It concerns me a lot. I haven't had sex or been fooling and sleeping around with anyone. So, it's not likely for me to be pregnant. I am really worried, what could have caused this? if I could be ill in any way. Please help me answer my query.

Update: i had been on a diet for the last few months then I suddenly was eating a lot again. I also had a lot of things on my mind i.g my visa processing and other matters.

Your menstrual cycle can be affected by your hormones and your mood - i.e if stressed for instance it can affect it.