My period is very regular and i always have a 31 to 33 day cycle, on day 20 of my cycle i noticed a tiny bit of blood on the tissue after i wiped myself, it qwickly turned to brown in colour and is still appearing on the tissue everytime i wipe myself, it has now lasted for four days. ive also had cramp like pains on and off for the past four days. This has never happened before and i am not taking any birth control as i have been trying to concieve. Is this a sign of pregnancy and is it ok for implantation bleeding to last this long? I have not takin a home pregnancy test yet.