Loestrin 24 FE...could I be pregnant?

I have been taking Loestrin 24 FE for the past 3 months and took yasmin for 2 months prior to that. With the loestrin I have had my period start on the first iron pill day each time until now... I'm done with all of the irons and still no period... The only time I have ever missed a period was when I was pregnant with my daughter. I took a pregnancy test this afternoon and it was negative, but it took 5 days past my period with my daughter to show a positive... I'm now 4 days late and still nothing... Has anyone else been on Loestrin and randomly missed a period when they are normally 100% regular? I don't want to start a new pack if could be pregnant.