Could i be pregnant?

Patient: I have been noticing that my breast have been sore for the past few days but only my nipples are sore and my breast do feel a little bit heavier, i also have been very tired for the past week, i did have a a period 3 weeks ago though.. and last week i went to my family doctor for a blood work pregnancy test but it came back negative… could i still be pregnant if it was too early for me to take a pregnancy test?