I'm mid 40s now and have had various gynae issues over the years. However, around the age of the OP I could have periods that came every two weeks or go missing for three months (I'm asexual). They did eventually work themselves out, still hate them (they wouldn't remove my insides at 27 as "I may change my mind" on having children, even though it's less than 1%)! I also have PMDD - which trying to get a GP to refer for was hellish. Good luck everyone.