Spotting after conception/fertilization??? how long does it take??

im a couple of weeks late since i was supposed to get my period. last time i had my period was march 20something. I want to know if I may be pregnant. My have been feeling tender for a while now but other than that no other signs of pregnancy until recently ive been feeling really tired and just a little nauseus but no big deal and today i noticed a little spotting? could I be pregnant? and how long after conception takes place could i start spotting? in other words how many weeks or days pregnant could I be? If I am?