This is the third time I've taken the morning after pill within the space of one year. Once last year in sept roughly, second time in April this year and the third time on the 17th of this month. I'm getting worried now because I'm not sure if it works and my period is due round this time and it hasn't come yet. Is there a chance that it didn't the morning after pill didn't work this time? I'm so scared.

I have friends that have experinced that. Take a pregnancy test. It will help. But after the first one, try another one, and then again a 3rd time to be extra safe. If they have varied results. Go to your gp and have a chat with him.
:) hope it helped.