Implantation question??!!

When would implantation bleeding occur? I was supposed to start on the 1st. Took two pregnancy tests, both neg. one before I was supposed to start and one yesterday. Usually when I get ready to start, I'm in fetal position and tears I'm in so much pain, I have very mild cramping, unnoticeable compared to what in used to. I just went to the bathroom and have a little bit of brown blood, atleast that's what I'm assuming it was. Is this sign of my period? Only time I've had brown blood was my last pregnancy that ended in a MC and got it the day before I MC. Advice please!? And thank you!