What am I doing wrong?

Hello, I have been using this website for around three weeks.  I am a medium built 5'2 female and I'll be 21 in a couple weeks.  I had always maintained 120-130 during high school even with horrible eating habits.  After getting my own place I gained until I hit 158.  I did the Atkin's diet for three weeks and lost 8 pounds.  I read more on it and decided it wasn't very healthy or sustainable for me.  I stopped dieting and just went back to more smart eating habits without really trying.  Although, I did eat quite a bit of processed foods, I lost another 10 pounds in the following weeks.  It was very easy to get to 140, but now I'm stuck.  In the three weeks I've been counting calories, I've lost and gained the same 1 pound.  I've been hovering from 1200-1280 calories a day.  I've had a couple cheat meals, but they usually get me to around 1700 or so.  I work in an office, but I park at the end of the parking lot, walk my dog a bit, clean, and cook daily.  Just today I've started a lifting program that I'll be doing 4 days a week.  It only takes around 15-30 minutes, because I don't stop for breaks in between the different motions.  I've read alot in the forums about people upping their calories and losing?  Any help would be appreciated, thanks! 

1200 is the lowest amount of food recommended for a totally sedentary, middle-aged female....  If you're not quite 21 and you're reasonably active I think it's probably a little low for you - but not by much.  Increasing your exercise is certainly going to help.  Do you drink enough water?  A litre or two extra per day can be useful

The most common reason for not losing weight is that you're simply eating/drinking more than you think.  For that reason, keep your food diary very accurately, weighing and measuring everything rather than guessing. It's good that you cook... packaged and ready-made foods tend to give inaccurate calorie-counts.  Fresh, wholefoods and food cooked from scratch are much easier to manage.

Another reason for a slow-down in weight-loss can be that your body has adapted to maintain your weight on less food.  It can help to plan a 'maintenance' day every 3 weeks or so to avoid that happening.  For example, this weekend you could have a day where you get a full 2000 cals.  Following that go back to 1400-1500. 

Hope that helps.

Thank you so much!  You're always so helpful, I see you alot in the forums.  I'll try increasing it a bit.  I do guess amounts, perhaps I should invest in a food weigher.  I only drink water 95% of the time.  Skim milk the other 3% and cranberry juice the other 2%.  I usually get 64 fl. oz. of water a day.   So maybe I'll kick it up to 1400.  Before calorie count, I was eating around 600-800 calories a day.  I couldn't believe it when I logged everything, no wonder I was so hungry.  I'll try this and hope for the best, thanks again.

You also may want to check your sodium intake. If you're taking too much salt in, you may have some extra water weight on you.  Also, not to be personal, but if you're around your period, your body will hold extra water weight making you plateau. It happens to me all the time.