no period/brown spotting then gone-- could i be pregnant?

well i had unsafe sex a few times in nov and dec, i missed my preiod all of nov, then in the middle of dec i started spotting brown, with a little pink now and then but it went away after like 8 days. my boobs really hurt off and on. and i am always tired. i took a few pregnacy test over the last few weeks but they keep saying im not pregnant, could the test be wrong? or is my body just not producing engough hgc? i also did a blood test but still noting....but i am never late and have never got brown spotting or anything like this..so please help....should i call the dr office and see if there was a low amount of hgc in my body? or what i am very lost about this whole thing i just wanna know....thank you all so much for your time