Did i have implantation bleeding??....could i be pregnant?

on dec.1st i had my period. it lasted the 5 days its suppose to. we did it on the 6th after we made sure every thing was good. he came inside me two times. after that night about 2 in a half weeks later i start not feeling good (CRAMPING, sick to the tummy. sore ) then on on the 26th i guess i "started again" but it was very light were i did not fill up a pad. it out a bright red on the 1st day then it started to turn brownish. it lasted up 2 the 28th(but it was on and off during them 3 days). my period was suppose to come a jan.1st but it didn't so I'm taking it came a week early....on the nth i took a first response test and it came up neg....all day today i had this bad headache and been waiting to sleep (ill get a little dizzy sum times).i feel really drained for the past two days usually I'm a happy person but lately every thing been making me mad (emotions are up and down)..... was the 2nd period an implantation bleeding??...could i be pregnant??