Missed period

So AF is 10 days past due. I know that i am not pregnant. I can say that bc lately like the last month my husband and i have not been having much sex. Not bc we dont want to but with our schedules and everything else we just never do. We do “fool” around though lol (sounds funny coming from a married 42 year old woman) so back to the problem AF is late and i even tested just to check but it was negative. With all this i don’t understand i am late im usually always right on schedule. Any ideas?