How many Calories are in Diet Sunkist orange soda? did I ruin my diet??

Im some what overweight and have stomach fat and I am on a low calorie diet to lose weight, I did good today, But I drank 2 cups of diet sunkist orange soda, it tasted really sugary, I didn't get to read the calories an info because someone already finished it and threw it away. So how many calories where in those 2 cups of soda I drank? And also, do you know if I can still lose weight if I drink diet soda once a day?