My period is a week late. pregnancy test was negative. my period is never late. what's going on?

Delay: Your periods occur because of changes in hormones within your system. While a lot of women have a period every month around the same time, there is variation from cycle to cycle. Ie – a period may come on a few days earlier or later and maybe heavier or lighter depending on the endometrium lining. It may come continuously or with intermittent spotting. These are variation of a normal process