I had cramps and I checked and down there was small amount of blood

On Dec 21, i had cramps earlier in the day (well, throughout the day), and then later at about 6pm, I checked and there was small amount of blood on my underwear.  This is when I was expecting my period. at around 8pm, I checked my pad and there was no blood. The next day, there was nothing, even when I wiped. Today is day 3 and there is nothing. Could I be pregnant? how long should I wait to test?