Why Do I Keep Gaining Weight In Spite Of Low Calorie Intake And Daily Exercise?

I typically get 30-60 minutes of exercise a day every day. I admit I’m not really on a diet, as I still occasionally eat things like, pizza, cheese steaks, hoagies, burgers, fried chicken and enjoy the occasional slab of chocolate cake from time to time. But I eat things like this in moderation, meaning if I’m going to have these things I eat little else throughout the day and double up on the exercise afterwards. In the beginning, I cut down on and even eliminated these foods and was able to lose 50 pounds, but when I started eating them again in moderation I stopped losing weight and was merely maintaining and recently I unfortunately started to put some weight back on in spite of the exercise. Shouldn't the exercise be canceling out whatever I eat anyway? Might the weight gain be the result of some other problem like a thyroid issue? You might get the impression that I eat these foods every day, but it’s really the opposite once or twice a week I’ll have them and the rest of the week I eat things like pasta and salad, alot of fruit and drink plenty of water. I’ve also completely eliminated soda and now drink only sweetened iced tea and water.