On Aug 8, I Had An Unprotected Sex With My

On Aug 8, I had an unprotected sex with my hubby but he didint cum inside me then I got my period on around 18th or 19th of August (as far as I remember). It was heavy and lasted for 6-7 days. After my period on that month we didint have sex. But on september 18 I got my period and it was a light period that lasted for 4-5 days. Im confused that if the light bleeding was implantation bleeding. Actually I have irregular periods. Is it possible that I am pregnant even if we didnt have sex befpre I got my period on september?