Morning sickness?

About a month ago I had unprotected sex,he came inside me and the next day I got the morning after (plan b) pill, then my period came straight after, it's only lasted about four days, compared to my regular 7 days that's a big difference.plus it came 3 weeks early? Now, a month down the line (when my period would of came) I'm throwing up? Morning sickness? Is there a chance I'm still pregnant even though I already got my period?