hey.. advice?

so i’m 14 and i started my period about a year and a half ago it’s change a lot since then it used to be very light for the first month and then became very heavy up until last month and it’s been shifting later towards the month slowly by a day each period (i hope that makes sense) so like it would always come one day later each month, anyway my concern is that i’ve missed two periods so far and i have definitely NOT been sexually active and i haven’t gotten any “before period symptoms “ and i’m getting worried.. any advice?