This may not be of any help but this happened to me once, I think I was around 16/17 and I went around 3/4 months without having a period. I didn't tell anyone nor was I sexually active and then one month it just came back. I just put it down to stress and my cycles just messing up a bit. Not long after I went onto the pill and haven't had a problem since. If you are getting worried I would just contact you're doctor ☺️