Period or implantation

Kerwine
I am 20 years old My period is suppose to be here in 2 days but for the past week I have been having really sore nipples and on Friday I had really light pink blood when I wipe but nothing on my underwear and on Saturday I have really light brownish blood when I wipe but still nothing in my underwear I am having back cramps I have had sex with my boyfriend but we use a condom and he does not cum in me took two pregnancy test both came back negative also I just got off borth control about a month ago so can some one tell me the difference between my period and implantation I am freaking out because I think I might be pregnant is it normal to spot before your period can someone explain what spotting is