Period late again??

Terra
Last month my period was 14 days late but then started and had a normal period only lasted 5 days usually lasts 6 but normal. Now this month it's already going on 7 days late again and hasn't started yet! Any ideas of why or what's going on? I took a pregnancy test last month when it was late and it was negative haven't taken one this month yet. Any ideas or advice will help!!