When I go to the gym, I gain weight. Muscle is heavy.
Just because you don’t lose weight does not mean you are not losing fat. It is an undisputable fact, that if you do go to the gym, you will be healthier.
Don’t concern yourself with weight, instead rate your progress by measuring body fat and your shape.
The last time I went to the gym 6 days a week for 2 hours a day, I ended up 25 kilos heavier than when I started, but I was much slimmer and fitter. Keep at it, it will pay off in the long run.
Pay close attention to compliments too, as you see yourself every day, you wont notice the change as much as someone who only sees you once a month.
EDIT: oh, and eating 1000 calories a day is not good enough, you need to eat much more. If you starve yourself, your body goes in to emergency survival mode, and will stop you losing weight because your body tries to keep hold of your fat to conserve energy reserves.
Figure out how many calories you need to eat using your weight, age, gender and height, for an active lifestyle, then stick to that. It will work eventually.