Which should I go by to determine my pregnancy week?

I had my last period on the 15 of May 2011. My periods are usually seven days long in duration. I had unprotected sex the weekend of the fourth of June with my husband. A week later I had what seemed like a period almost three weeks early for a day and a half. It went from heavy to very light pink/brown. We also had unprotected sex that weekend. From a previous pregnancy I was told that this does not count as a legit period. I have used pregnancy calculators it says six weeks if counted back from the one in May or almost three from the strange one. I'm confused as which to go by... In the meantime I've had swollen breast,bloating,morning sickness... Which do I go by?