The old saying 'if it hurts it must be doing good' certainly doesn't apply, and you must cut back on effort, pace, and distance. Early recognition and appropriate action will pay great dividends. I have been swimming regularly for three years, two or three times a week, in an attempt to lose weight, but I have not been successful. I am trying to lose a stone. This is an old chestnut, familiar to most athletes and non-athletes alike.
Real growth stops in our mid-twenties and thereafter the 'battle of the bulge' begins.
Exercise is usually a great assistance to weight loss, but conversely if muscle bulking is a feature of your exercise programme you may actually gain weight. Exercise in itself isn't usually the answer to weight reduction, and you will have to reduce your calorie intake. This can be difficult while you are balancing your energy levels so that you can still train without undue additional stress. I recommend a fat-free diet because it is relatively easy to achieve. You will feel better and have less heartburn and indegestion, and will probably sleep better too.