I am 18 and I never have had my period and I grow hair in weird places for example under my chin and my body hair grows really fast why is that

Have you seen your doctor about it? It would be a good idea to do so if you haven't. There are some conditions that may be a cause, for example, PCOS (polycystic ovary syndrome).

Have you been pregnant all your life? :-/ Or maybe you're a late bloomer but this doesn't explain the body hair... it's growing fast because of your genes, maybe it runs in your family or something.