Why do I feel depressed after a workout?

I've recently taken up running to increase my cardio and I have noticed that after I work out I feel very depressed. I have cut most carbs(sodas, bread, rice, ect...) to get my diet in better order. I do have chronic depression, but I am not sure how much that would factor because I have noticed that the workout sessions specifically trigger how I am feeling. I am a little worried because I don't sabotage myself when I am feeling down.