I had sex about a month ago and my period came on 3 days later and I was 2 days late, but that has been common for the last 3 months. Its now time for my second period to come on and its one day late. I was just wondering could I be pregnant even though my period came on 3 days after I had sex a month ago.

Probably not. You're probably just late again. That happens with females as they get older their period become more irregular. But you can always take a HPT to be sure of see your doctor.