What do you think of this?

I took plan b an hour after the incident happened. My period came a lot earlier than expected - it came a week after I took the pill. Now, it has been one week since my last period and I noticed dark brown blood on my underwear.My stomach was hurting me today like my period is about to start again... I am terrified. Am I having my period again? Please, if this has happened to you before, help!!!