New to charting

Jessica • Married 29/09/18 👰🏼 2 angel babies 👶👶 🌈due march 2020

Is anybody able to help? I have no idea why my temps are so up and down? Defo having ewcm but all my OPK are negative. Last month i ovulated on cycle day 18, i know this doesnt mean it will be the same this month but my OPK are very negative

Thanks in advance