Confusion with due date

Hi please can you give me some advise!!

I had a period on 30th May 2011, I had unprotected sex on 5th June 2011 however I took the Morning after pill on the 6th June 2011.  I then had some bleeding on 11th June for a couple of days.  I then had a period on 1st July.  My confusion arises as I am now 16 weeks and 5 days pregnant however I was admitted early on in my pregnancy and they did an ultrasound and told me I was 5 weeks ( only a yolk sac and no heartbeat) I was asked to go back a week later to see if the pregnancy was progressing which it was as they seen a heartbeat putting me at the 6 week mark, which ties in with my last period of July 1st.  I then went for my 12 week scan and they said I was 13 weeks and 4 days and this was definate and would not change.  Is there any possibility I could be pregnant from the unprotected sex I had on the 5th of June or am I ok to think that I conceived after my last period of July 1st, I am driving myself crazy with worry.  Any help or advice would be great.  Thanks.