Period or implantation

Kerwine
I am 20 years old My period is suppose to be here tomorrow  but for the past week I have been having really sore nipples and back cramps 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 and today same thing light pink blood when I wipe but none 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 one on Thursday and Saturday both came back negative also I took birth control last month for 3 days and got off of it because I was having really bad side effects I also took the plan B pill one day last month so can some one tell me if this is aunt flow or implantation i am freaking is it normal to spot before your period when should I take another test