I can't remember the date of my last period but It was mid August,then I had unprotected sex on the 24th of August 2012,after that I got my period in September for 3days,since I ddnt have sex,now am confused with my EDD because I haven't given birth until now.what's might be the problem?

If your last period was September 2012 something - obviously - is a problem. You need to see a Physician.

If your last period was in September, you aren't due until sometime in June or July. I'm unsure what your question is.