If you were drinking coffee before the Master-Cleanse your headache could be caffeine withdrawel which I know from my own experience are killer headaches. If you feel fine I reccomend staying on the cleanse. don't worry about those two crackers and move forward, but know that maybe in terms of cleansing effect you might be a day behind. (re caffeine withdrawel. I sometimes had a cup of green tea (not on official cleanse) to avoid the harsh withdrawel headaches)
great luck to you