All you need to do is to start loosing overall fat in the body by reducing the number of calorie intake every week. You also need to participate in cardiovascular exercise for about 5 days every week to burn up the excess calories in the body. Check out http://www.livestrong.com/article/27805-reduce-stomach-size/ for more particulars.
You don't have to do sports to get rid of a stomach ache. Usually the best thing to do is to lay down and get some rest and try to lay off of the soda. I went almost a week with out soda and felt healthy though I gave in and had one last soda ha , ha the key is to drink water you will feel so much better ! and a lot healthier too.
With all due respect, stop drinking soda and other carbonated drinks. They cause bloat and weight gain. You will notice a difference and when you do, take up a sport you want to. No one but you knows what types of sports you enjoy. Have a good day.