3 days late bfn? Please help!

AF was due the 18th and no sign of af and I've took 5 tests and all bfn. The only thing I did different last month is I took evening primrose oil from start of af until positive ovulation test. Could that have delayed my period? Has anyone had any experience with taking it. I'm freaking out BC af is like clockwork. I have a 24 day cycle. Any help would be very appreciated. Thanks ladies.