Hi! You should first ask your doctor about this, or a fitness instructor.
What I can say though is that if you're exercising a lot but not losing fat, that's an indicator that the kinds of exercises you're doing are sub-optimal. You should incorporate both strength training and cardio, with an emphasis on strength training. Building muscle with both help burn fat off and improve your muscular physique, or in your case, tone up the abdominal and pectoral area. Go to a gym to start a muscle building program or do it at home with a home workout program. As for cardio, do it after you do your strength training, because that will burn off the fat cells that you released while doing strength training. You can do whatever cardio you want, like biking or jogging. The cardio style I recommend is HIIT, or high intensity interval training. You can look up what it is and how to do it online, because it's too extensive to cover here. Those are the basics for exercise. You can't just sporadically exercise here and there and hope to burn fat—you have to have an actual plan.
Take a closer look at your diet, too. Is it actually as healthy as you say? Are you eating plenty of vegetables and drinking a lot of water? Are you eating a lot of sugar, refined carbohydrates like white bread, and crappy processed foods? Your diet should be mostly whole, unprocessed foods. Have a protein and a vegetable at every meal, with either a fat or a carb, but not a fat and a carb together. Snacks can be raw nuts and seeds, fruit, vegetables with dip, etc. I trust this advice was helpful to you.
