I am 12 days late on my period and pregnancy test say im not pregnant what do i do? its never been late

Wait and hope...: Pregnancy is the most common cause of a missed cycle. Another common cause is simply and anovulatory cycle, where your ovary does not release an egg for the one cycle, and thus no period comes. Wait for the next months scheduled cycle and see if the period comes. (remember though, if ovulation starts again you will be able to get pregnant then). If second misses, see the Dr (GYN).