No period, no prego

month 4 of trying. had sex at the right time. Period due today but no sign and negative pregnancy test. Didn't get to surprise my hubby for his birthday yesterday. Maybe a Halloween surprise ?? Today's test was negative so I doubt it. Very discouraged. A few days ago I had some cramps and lower backache but absolutely no symptoms today or yesterday. anyone else get a negative prego test when their period was due and later have a positive? I'm going to test again On Halloween If af doesn't show by then.