Does Delayed Period While On Althea Indicate Pregnancy?

I am on althea for the past 4 years. My last active pill was on March 7. Last month, I had my period on February 12 so I was expecting that my period this month would be also Mach 12 ( or is my expectation / calculation incorrect?). Until now, I have not yet bleed. Am I pregnant? Can I do a pregnancy test tomorrow? I am not sure if I have taken the pills on time but I am sure I did not missed it. I have never missed any bleeding for 4 years I have been taking althea. Please Help