Way to much cardio and not enough weight training.
You only need three 20-minute sessions of cardio each week (try upping the intensity) and three 45-60 minute weight training sessions (time to up the intensity, i.e. weights). All that cardio is most likely eating up your muscle, thus the reason you are gaining weight! No muscle means a lower metabolism which leads to fat gain over time.
It's great that you are dedicating yourself to training! But as mentioned above, you're dedicating your training in the wrong areas. A little redistribution, and you will begin to gain lean muscle mass and start burning up the fat.
Don't be afraid to lift heavy weights. Heavy weights will make you lean and shapely, not big and bulky. In fact, light weights in the 12-15 range will most likely increase overall muscle mass much faster than heavier weights and lower reps.
Now, since you also work a desk job, what you eat is just as important. See below.
You should never diet. You shouldn't think in terms of dieting. You should always think about your health and making behavioral changes to your lifestyle for long-term results. Being healthy means eating healthy at least 90% of the time.
Okay, having some sweets maybe once or twice a week in addition to your healthy, daily diet is fine. But having your sweets in place of good foods is a no-no. And, you should always restrict the sweets, pizza, processed foods, etc. Even one sweet thing a day will add up over time. Before you know it, you'll gain weight even with everything else remaining constant.
So clean up your diet. Save the sweets for a cheat meal on the weekends (in addition to your healthy foods). Don't skip meals. Eat every 3-4 hours for 5-6 meals a day. Eat protein with every meal. Eat most of your carbs (oatmeal, whole-grain bread, veggies, fruit) earlier in the day and taper them off in the afternoon and throughout the night.
Research shows that the body handles carbs best earlier in the day, but not in the afternoon and night. So eat healthy meals at night consisting of protein and good fats and fiberous veggies (anything green, tomatoes, mushrooms, onions, salads, etc.). But skip the bread, pasta, rice, etc.