emergency contraception and birth control

hi im 17 and have been on the pill for 2 months. Last Wednesday my boyfriend and I had unprotected sex twice, but I was worried so I took next choice the following day. Two days later (yesterday)we had unprotected sex twice more. I have not missed any pills, but I have taken a few (on weekends) an hour or two late due to scheduling conflicts. Today I feel nauseas and once more am paranoid. Granted the pill stops you from ovulating, but if I were to be, this would be my most fertile week. I have not had any spotting, but none the less I am concerned. What are my chances of becoming pregnant?