Why does my period come on and off ?

Sydиєу • I'm 16 😌 I am very curious , classy never trashy! 👑 my body changes are unnatural at times 😑 it sucks being a woman !
My period comes whenever it wants to it might come next month and sometimes it's late I haven't had my period for about 3months ! I'm a virgin & it's really confusing,What process is this ?