I been on birth control since September of last year I had sex on January 4 and my period was supposed come on on the last week in January after my sugar pills and it didn't I missed one pill after that and took it the next day and also I would be at work without my pills and didn't take it at the right time I would take it when I got home it is now febuary 10th and it still hasn't come on i took a pregnancy test on the first week in February and it was negative. Could I have missed my period because I missed one pill?