confused

Hi, i am a 21 year old female and i am kind of confused.On feb. 24, my bf and i had unprotected sex. on mar 4 my period came on, not to mention it was three days early. on the fifth, i was having severe stomach pain so i went to the ER. they did preg test with both my urine and blood. both came back negative, but today is mar 9 and i am still bleeding very light, almost a pinkish brown color. usually my period is only four days and has a constant flow. but this month it was very light and when i was in pain it was extremely heavy. i wanted to know was it a possibility i could be pregnant, and was it to early for the doctors to tell when they performed the test.