What Causes Late Periods?

ive missed my period. im about 6 days late and i had nothing but like this brown discharge a darkbrown discharge on one day i had lightbrown/pinkish discharge. and then like a light bleed and the next day just brown discharge. i havent had any symptoms or anything but i have been a bit under the weather because my dog died and stuff. help? i still feel the tiniest sharp pains in my boobs and below my ribs