4 to 5 lb difference in one day?

I can put on 2lbs after drinking a few cups of tea, I dread to think how much i'd weigh after a full day of eating and drinking.
Weigh yourself first thing in the morning, after the loo and before eating and drinking anything.

Scooby has some enlightening information about weight fluctuations:

http://scoobysworkshop.com/how-to-weigh-yourself-accurately/

The correct time is the same time whenever you're weighing yourself - doesn't really matter if it's 10AM or 2PM; just so long as you consistently weigh yourself at that time

Most of us, first thing in the morning, have fasted the longest & are the most dehydrated we'll be all day, because we just spent 6-8 hours not eating or drinking anything.

Furthermore, believe it or not, when we lose weight, most of the weight "goes away" not through excretory processes as many people assume, but through . . . exhalation. Yup, you burn food or fat, and it leaves just like smoke out a chimney. You can look it up. And first thing in the morning, you've just spent 6-8 hours doing little else but exhaling.

If, additionally, you weigh yourself first thing in the morning after, um, relieving yourself, then your bladder and digestive tract are about as empty as they're going to be all day.

During the day, you eat, you drink - most of that's still hanging out somewhere in your body when you weigh at the end of the day.

Look at it this way: Weigh yourself right now. Note the weight. Drink 2C (measuring cups) of water. Weigh yourself again. If your scale's accurate, you'll weigh one pound more . . . because 2C water weighs about one pound.

Get over the idea that you have "one true weight". You don't - it fluctuates all the time. There's more urine in your bladder, or less. You're holding more water weight in your body tissues for muscle repair after exercise, because you ate extra salt or carbs (even if still a healthy amount), or because you're a woman & it's some particular time of the month. You have more undigested food somewhere in your digestive tract, or less. I could go on and on.

Weigh yourself first thing in the morning, under the same conditions. Track that. Expect fluctuations, maybe as much as 3-5 pounds occasionally, even first thing in the morning.

Look for a downward trend over a period of time (days to weeks), if you're trying to lose weight; an upward trend over a period of time, if you're trying to gain weight; or a level trend over a period of time, if you're trying to maintain. That's what you want.