Help!

Alex
I'm on my 3rd week of taking Levora birth control and I was suppose to get my period a couple of days ago. The first week of taking it I would take it in time everyday but the second week I would be a couple hours late to take it because of my crazy work hours. My last period was June 5-8 and I started birth control on the 20th of June.  
We did not use a condom once and I took plan b the next day cause I wasn't sure if my birth control would work because I took it late for a couple of days. I don't know if my period is just being pushed back because of the day I started or if I should be worried ?