Am I Having Delay In Period Due To Having Norethisterone?

Hi, I took noristherone to stop my period while I was on holiday last month. When I stopped taking them I came on 3 days late. I have not yet got my period for this months, and I'm never late. I did a pregnancy test after the 2nd day of missed period but it was negative. I'm panicking as I am never late and wondering the test was right. Please advvise if this pattern is common. Thanks.