You are going to be fine! Just keep doing what you are doing! You could possibly be gaining muscle, and your weight can change by 2 lbs within a day, so don't take that too seriously. I personally weight myself at 9 pm, every other night. Sometimes I wait a whole week before weighing myself. Try not to focus on that number every day! Try to space out your weigh in's....it might help!
Listen to chula1993, she's right. You're not going to consistantly lose or even maintain your weight day to day. Hormonal fluctuations, water retention, excess sodium, lack of bowel movements, any one of those factors can and will contribute to temporary weight gain. Don't panic about what the scale says. I can ASSURE you, you did not put on 3 lbs of fat overnight. If you look at it from a mathematical point of view, roughly 3500 calories = 1 lb of fat. In order to have gained 3 lbs of fat, you would have had to consumed about an additional 10,500 calories of what your BMR burns as well as what you're burning during your workouts which is not easy to do. If you're eating about 1500 calories a day on top of regular exercise, you don't have to worry about gaining any "real" weight. You weight gain is probably just water retention.
By any chance are you due for your period or do you have it currently? Because if you are, that would explain a 3 lb gain. I know I can easily put on 2-5 lbs right before or during my period and then my weight will go back to normal a day or so after my period finishes.
Also, consider weighing yourself only once a week. Weighing in every day will only drive you crazy because you weight is definitely going to vary day to day. Like chula suggested, once a week is more accurate.
Don't be discouraged. Just be patient and keep doing what you're doing! It's working and even if you don't see the results you expect every single week, your hard work will pay off big time in the end as long as you continue following your plan!
If you are weighing yourself on a daily basis, you cannot look at that for your weight loss. There are too many variations, such as water weight, bloating, different foods that you may have eaten. It is better to weigh yourself weekly to get a true loss/gain weight. Also, your typical weight loss from one week is usually accounted by your activities the week before that. The extra exercise that you have been doing will catch up to your weigh in next week. And, you may have hit a plateau, depending on how much weight that you need to lose. If you did, or if you didn't, don't get discouraged!! Keep up the hard, awesome work! It will take time but you can do it! Also, try to get outdoors to throw some variety into your weight loss effort. Keep working at it! Good luck!!