What Are The Side Effects Of Plan B Ipills?

I took the the medication Plan B on 10/30/10 because I was worried that I had unprotected intercourse while I was intoxicated and was not taking my birth control at the time. I got my menstrual cycle 2 days later but it only lasted for a 3 days and then went away. I started my birth control a week later and received my menstrual cycle again for just one day and I've yet to have it again. I know I'm not pregnant because I found out after taking the Plan B that no intercourse actually happened but I have been really stressed lately which might be effecting my cycle. I just wanted to know if it is normal when you take Plan B to have irregular periods from it?