Implantation bleeding or period?!

Hi ladies, I miscarried in January at 13 weeks (our first). We have just begun trying again. I am 5 days late for a period and have tested numerous times (much to my embarrassment) all coming out negative. I have been having cramping on my left side (similar to what I felt the first time around) and today I had very, very light pink/brown blood when I wiped. I did not have implantation bleeding with my first pregnancy. My question it possible to have implantation bleeding and a negative test? Has this happened to anyone else? Or is this just my period coming? So confused and anxious. Thanks in advance :)