Implantation Bleeding?

Ok I feel slightly crazy for even asking this butttt.....my "period" came on time, however it was only heavy the first day and the past two days it has been basically spotting old stuff here and there, which is odd because my periods normally last 5 days with the last day being the only light day. In addition I have had tons of cramping (but the kind of cramping I've had with my last 3 pregnancies) so that is also throwing me off. I took a pregnancy test last Friday and it was neg and my period lightly started later that day so im pretty sure I'm not pregnant but my period was super odd so I thought I'd ask about it. Also, I have never experienced implantation bleeding with my other pregnancies but have always lots of cramping like I am now. And yes I could take another test but I don't have any and feel silly buying one of this is a complete long shot. Any thoughts?