Implantation or period??

I am currently trying to concieve (conceive). I am a mother of a 2 year old, this is our second month trying. WIth my last pregnancy i was due for my period on a tuesday and on the sunday before i started spotting, which i just thought was my period coming early. Didn't pay much attention to it. Then a week later this weird feeling came over me, that i was pregnant, meanwhile i was still spotting. So i was like no.. i can't be pregnant, but i went to the store anyways and got a test and took it and instantly it came out positive... well now, i feel like I am in the same boat. I always start on tuesdays...always!! and yesteday on a monday i started spotting. it was redish pink at the beginning then it has turned more to pinkish/brown sometimes red.. it is only there when i wipe. doesn't get much on a panty liner. I took a test yesderday and today and both came back negative. I am wondering how soon if this is implantation would a test come back positive. I just feel like this is the month, and that i am pregnant. I am kinda crampy though and feel very weak and shaky almost... So is this implantation like my last one or do you think that this is my period just coming a day early to through me off... HELP! :) When can i test?!?!? *hoping for a BFP!*