What Causes Short Period After Taking Morning After Pill?

I took the morning after pill three weeks ago, about 2 days after my period ended. I then had a period the week after. It was shorter than usual but still a full period. I have had sex about three times since then, all protected. It is now a week and a bit after that period and I have very very light brown discharge. Is this ovulation? I'm not sure what to do and am really panicking. Thanks.