could i be pg with the pullout method

My bf and I always use the pullout method. He is really cautious when we have sex! Last period June 5TH for four days. Then on June 13th for 4 days I had dark brown discharge. Not a lot but needed a liner. we I have taken 2 pregnancy teat both neg. late week. Also take in account I am irreagular but for the past several months I have had a cycle. Today I have been feeling nausea. Could I be pg?