Before adding another hour of Combat a day, I would say vary your routine throughout the week. Add a Body Pump, BodyFlow/BodyBalance and/or an RPM class. Changing things up will strengthen and work ALL your muscles and make you less prone to injuries (from repetitive movement, overuse, overtraining certain muscle groups while neglecting others, etc.) If you're experiencing joint pain from the impact in Combat, then adding another hour of it is asking for injury.
Nutrition plays a HUGE role in losing weight. There are lots of great resources on the web for learning more about nutrition. First you should calculate your Basal Metabolic Rate (BMR) which is the number of calories your body needs each day just to function. (If you do a Google search for BMR, a website comes up that has a calculator. It's very easy.) Once you get that number, don't go below it! Calorie restriction will starve your body of the fuel you need to power through your intense workouts. Eat to lose! Think: lean proteins (chicken, lean beef, salmon, or tofu/soy if you're vegetarian), lots of fresh veggies and fruits, nuts, and complex carbs like whole grains and beans and sweet potatoes. Eat for performance. There's no "performance fuel" in a bag of chips, a soda or a cookie. (Though everyone deserves the occasional treat:)
Go easy on yourself and remember that you are only 25! You have started the journey much earlier than some people. Don't think of it as a sprint or a strict timeline. Just get on the right path (which you already are) and keep taking classes, do what you love, be kind to your body and give it the right nutrients and water and sleep (hugely important for weight loss!) and the scale WILL move!!!! It's a guarantee!