Missed period

I’m not sure if anyone will be able to help me but I’m a 15 yr old and my cycle has never properly been the same. I’ve missed months on and off. But just recently, I haven’t had a period in about 3 months. Idk if this is normal or not and I definitely know I’m not pregnant as I’ve never had sex and I’m single. Has anyone got an explanation about missed periods or anything??(I’m also going on holiday this Monday, what are the odds of my period starting then?)

P.S. I’m super scared that there’s something wrong with me.