Can the allergy pill allegra cause a missed period?

[Samantha C]

I've seriously been regular since I was 12 years old and have never once missed my period. I recently switched from singular to allegra, because my asthma has been in check; however my period is about 3 weeks late considering my cycle is usually about 23 days. I'm definitly not pregnant and I don't know what else could have possibly caused this irregularity so I was just wondering if anyone else has experienced this.