Do you get cramps before your period?

this is a really stupid question for me to ask as im 26, but i've never had it before the period. i ask because the past 3 days i have been spotting a very light discharge on and off every 4 hours or so hardly anything really, a little smudge. I'm not sure if this is an early period, im due to come on the 3rd jan. i usually get cramps about 3/4 days into my period, not before. i dont usually spot like this either, im very regular (28 days). i am trying to concieve right now, but implantation normally lasts about 2 days at the most i think. today the discharge dissapeared, but reappeared now a few hours ago. i took a preg test today but i got a neg. does anyone know what could be causing this? or how i work out my next ovulation/period date? thank you!