Going on 6 months

My last period was at the beginning of January. I’ve always had irregular periods but never this long. My doctor believes I have PCOS but when doing a scan found no cysts. My periods are not painful, they just never come. Recently I started noticing cramps, but still no period. Any clue as to why this is happening. I’m only 20 years old so I’m not worried about children at the moment but I’d eventually like to have children and this is something I really worry about 😞