Not been on contraception for 18 months now, periods like clockwork 27 days (one time 26). I am essentially 3 days late on my period, do not feel like it's coming. Mild cramps every now and then, no other symptoms besides slightly nauseas every now and then (not uncommon for me) & not sure on ovulation. I should have came on on Sunday. Would a positive test show by now? Should I wait?