So I had sex on like the 14 of August and my period starts on the 5 the of month and its now September 14 and I'm pregnant so howfar long am I?

Nobody can know for sure... seriously... all doctors can do is guess. When you are far enough along to guess a due date its usually back 9 months give or take 2 weeks... so even then that can only guess to within a one month window.

Is that the only date you had sex ?

What was the first day of your last period?