Yesterday the scale said I weighed 207 lbs today it says I weigh 200 lbs how is this possible?

yes. Part of it is measurement error, the other part is body weight fluctuations. There are a lot of factors that contribute to both, but when they align, the measurements can be way apart. If you are going to weigh daily (and I personally recommend it) you need to do what you can to reduce variability and then use trend lines (regression) to track weight.

If you don't want to go to that trouble, then weighing daily means nothing and you need to weigh monthly or so.

have to weight at the same time every day preferably in the morning after you do your business. ive weighed as much as 3 pounds more at the end of the same day. and also my boyfriend can looses weight very easily especially water weight, he can go down 5 pounds in a day easy if he tried. and if its the beginning of your wight loss and if you have alot to loose its possible.

Yup, totally possible.
It's as people have suggestions water/digestive fluctuations. I weigh myself every morning before I shower to look for trends. Sometimes for fun I weigh myself as night and some days I'm almost 10 lbs heavier and sometimes I'm lighter at night.

You weighed in the evening? Evening weights fluctuate a lot. Even people at low weights can fluctate 5 lbs throughout the day depending on what they are drinking/eating. So when you compare weights at different times, you're results won't show as accurate as they could be. Weighing daily is fine, just make sure it's morning at the same time.

You weigh more after a workout BTW. Your body produces lactic acid (if I remember right) when you workout and this causes you to weigh more just post workout. Not the best time to weigh as it's really not an accurate picture. Also, yes, fluctuations happen throughout the day normally. If you weigh in the morning, before eating, you'll likely be the lowest weight of the day. Weigh at mid-day, after lunch and you'll probably be up several pounds. For the more accurate results, you should really designate a specific time to weigh. I used to weigh every day and I challenged myself to get in the habit of only weighing weekly. I love it now, though it was hard at first and I'm still tempted sometimes, but I see a more complete picture and focus more on my health than the number. It's very freeing actually.

I personally prefer to weigh daily. I know that fluctuations will happen so I am prepared when it shows higher one day etc. My period may be coming so I am retaining water, I might not have needed to use the toilet yet so I could have solid waste still there from dinner the night before, I might be retaining water because my muscles are healing from a strenuous workout. Its never going to be straight downward loss because there are too many variables. For instance, if I eat bread products, I know that I will probably see a temporary water gain for a few days because that is how I work. I can be fluctuating 10 pounds in a day! I might be my lowest weight first thing in the am, have a glass of water...weigh myself at the gym an hour later and see I am up 2 lbs, not counting clothes. And, don't forget, food and water are heavy! A liter of water is like 2 pound or so!! And you are carrying that around...you are not going to pee or poo the whole thing out right away. It has to process.

The reason I like to do it every day, after I wake up and do my "business" and before I eat is so I can see and keep track of the downward trend. Makes it easier for me, seeing the ups and downs and knowing (and SEEING) the weight in a downward movement.

Totally possible, particularly if you had caffeine, alcohol, cold medicine, or any other kind of diuretic yesterday.

I once lost 5 lbs overnight thanks to a bottle of white wine!

It's best to weigh yourself at the same point in the day every time you weigh though. The weight of the clothes you're wearing (sweaters weigh more than tshirts, denim weighs more than linen) is a factor, as well as the food and drink in your stomach. A cup of water weighs a half a pound, for example - so if you weigh yourself, then drink a 20 oz bottle of water, you'll weigh a pound more. Most people choose in the morning, before showering, after using the bathroom, while nude, to eliminate as many variables as possible.

A gallon of water is 8 pounds, so totally possible.

Don't focus on the numbers of any scale. Ask yourself:
1 - Did I make the right healthy decisions today?
2 - Did I answer question #1 honestly?

The numbers on the scale will do what they do and I for sure do understand how seeing the numbers go down impact my own motivation. But weighing daily will drive you crazy because of normal body operations. I don't know about you but I don't need to second guess myself just because the scale said something I wasn't expecting every day. I look for trends and for me weekly weigh in is sufficient to establish RELIABLE trend line downward. At the end of each day when I wrap up myfitpal log, I evaluate my effort (or lack of effort) by asking myself the 2 questions at the beginning of my comment. That's all.

Where is your scale?
I think a lot of people overlook the importance of having your scale on a smooth, flat surface such as hardwood or tile.
When I first started paying attention to weight, I couldn't figure out why my weight would fluctuate so much in a day, or even in multiple steps on and off. Or why I'd be so different on one scale from the next. My scale was on a flat surface with thin commercial grade carpeting in the office gym. Once I moved it to the tiled bathroom floor, it became more accurate and 100% consistent. All the steps off and back on didn't change the numbers. I did some research on this when I first started my weight loss journey and the addition of even thin carpeting can cause the numbers to be off by as much as 7 or 8 pounds. In my case, it was off by as much as ten sometimes on my bedroom carpet. Home-use scales need a flat, level, non-carpeted surface to be accurate.

Weight can fluctuate up to 10 pounds in a 24 hour period.

I weigh daily... but every morning, after using the toilet and right before jumping in the shower. I find that this gives me the most accurate number and with having that routine I feel confident that I'm getting pretty good results. It took me a some trail and error to find a good time to weigh myself but that seems to work. However, I only "Count" (or log) my Friday number (Maybe Saturday if I'm on the fence weight loss wise or I've been sick). By doing this I see more weekly improvement in weight loss and don't freak out so much over daily changes, both up and down. I also measure several points on my body every week and take that into consideration. I know that the scale is only a number and that the measuring tape gives me more info anyways!!

Good luck!!