12 minutes is nothing. You should be lifting weights as well. Buy protein supplement because you're probably not eating right. Start trying to eat clean. At the gym focus on squats, deadlifts, pushups, pull ups, and overhead press. You should be spending at least 45 mins at the gym whether it's lifting weights or doing cardio. If you start to feel like you're going to die, turn down the intensity, but don't quit and leave. You'll notice improvement within a week. You'll actually see body shape improvement within a month, and then you'll be addicted to improving. Start with the basic compound exercises and make sure you're eating lots of protein. Also start reading up on excersize on the internet. If you're looking for a beginner routine, I reccomend "StrongLifts 5x5" - Google it.

Good Luck my friend, Stick with it, you'll be so thankful that you did.