I'm 5'7" 123 pounds and just trying to get to 120 or 118. This week I ate over my calorie allowance almost every day, going into 1850 cals and over 2000 and I've either maintained doing this or gained a little bit. Well I had enough and yesterday ate 1300, thinking surely I'd lose a little bit especially since my body isn't used to eating so little. But nope, I maintained 123. What gives?? Will I just poop it all out later, am I retaining water, or am I doomed to gain weight no matter WHAT I do? I don't think I can make myself do 1200 a day again, that was torture. Is it really my only option for weight loss? Btw, I work a very active job so I shouldn't need to over excercise as well.

You're not doomed to gain no matter what. Don't worry; little mini-plateaus like this happen ALL the time.

When I'm stuck on a plateau no matter what I do, it's usually because I'm retaining water from my cycle. Remember, too, that weight loss is not linear. Our bodies are complicated things that any number of variables can affect, from the things we expect (like food, water, etc.) to things we don't (how much sleep we got the previous night, our stress levels, the weather, etc.). Our weight also tends to move surprisingly little based on the choices in the immediate 24 hours. Instead, they tend to ride the trend of our choices over a long period of time. So eat in a deficit, exercise, drink lots of water, watch your cycle to make sure it's not because of that, and you'll lose weight just fine. I'd also recommend taking measurements, since the scale can be such a liar, measuring not just fat, but our bones, organs, and yes, water weight. The tape measure is much more honest.

I do feel obligated to note that I see you're trying to lose to a BMI of 18.5. Just be careful, okay? That's pretty low.

1 day isn't enough to see whether or not you've made progress, because your water weight fluctuates from day to day. Give it 2 weeks to see if you're making progress.

Are you sure you need to lose weight? You already weigh less than most people who are the same height as you. If you think your body looks fat, the problem might be lack of muscle rather than too much fat. Even if you spend most of the day walking, you're not going to build a lot of muscle from that. I would recommend doing some strength training exercises, if you don't already do that (it'll be useful for both building muscle and burning fat).

I think it's more important to focus on eating healthy foods, rather than just cutting calories. Eating the right foods makes it much easier to reduce body fat. If you want to post a list of foods that you eat, I might be able to suggest changes that you can make.

I'm similar height and weight with you and I have the same frustration sometimes, especially if I have a lot of fiber, like popcorn, to fill me up in the evening. And sometimes I'll weigh less in the morning if I eat a ton of total junk calories. It is hard that you can't really measure whether you're making progress very closely since you can't ever exactly tell what's helping, but keeping calories down does help over time.

I agree with MJF. One day really isn't enough time to see results. To lose a lb, you need to burn 3,500 calories. I'd stay below your recommended calorie amount to maintain for a week and then see where you end up.