Can Nordette Be Taken As Emergency Contraceptive Pill While On Althea?

Hi I have been using Althe pills as ocp since October 2014 and it has been very effective for me because I always take it regularly on time. I started my most recent pack last March 26, 2015 and finished with the last pill last April 15, 2015. But during this period, sometimes I miss a pill but immediately take it the next day, which makes me take 2 pills in a day. I may have done this twice in this period. But I finished the pack last April 15. I had unprotected sex April 16 and my partner ejaculated inside me. This date is within the seven day pill free period. I do not recall the exact date of my last period but I think it was around March 20, 2015. I am worried that Althea would not be effective for me this time because there were days when I missed a pill. So, I want to take Nordette as ECP today April 17, 2015. Would it be okay to take it on top of my Althea consumption from March 26-April 15? I really want to be safe from unwanted pregnancy thats why I want to take Nordette. Please advise me. Thank you.