I have to completely agree with the two posts above me! When you start eating more, there will be more weight of the food in your body AND I'm pretty sure that when you eat a bit more carbs (and I'm sure some of the extra calories will come from carbs), you end up storing more water in your cells along with the extra glycogen, or.. whatever

Something sciencey!
And it is true, if your weight goes back up a bit it is not necessarily fat. With you eating at 1200 calories and your body being at a constant deficit, it has surely had to let go of SOME muscle that might start to build back up now that you have some calories to work with. In my case, once I got down to my lowest weight (~93 pounds) and my nutritionist helped me to start adding back healthy calories, she told me that my body also needed to rebuild/repair my organs.. o.O
You might be interested to know though, that when I got down to about 95 pounds I was eating 1200-1500 calories per day, and exercising 5-6 days a week for half an hour. I increased my calories SOMEWHAT slowly (by 100 calories a day each week), and ended up at 1600-2000 calories per day and exercising only 20 minutes 3-4 days per week. My weight spiked up for a bit, but then it kinda settled around 98 pounds. My metabolism was NEVER very fast before I lost the weight, and hopefully my experience will at least provide some sort of hope.
You'll do great! Just make sure you give more calories an honest chance and don't overexercise, because if you let a tiny scale increase scare you too much you might get unnecessarily stuck at this caloric intake forever! And you could be eating more, and maybe feeling better
