I have weighed myself everyday for months and your weight really does fluctuate a lot from day to day,
for example you follow the slim world diet i do Extra Easy and you have a large portion of boiled rice or a large portion of spuds for tea, the next morning you can weigh as much 2 or 3 pound more than you did the previous day which can be depressing.then two days later you can drop 4 pound,i think you do need to keep portion sizes down though ...