Excess of anything is bad for health. Soft drinks do not cause health problems unless they are consumed excessively. An occasional consumption of soft drink will not harm your health but if you replace it with a healthy diet and more nutritious drinks then, your health will get affected due to poor intake of nutrient dense foods. Soft drinks provide only empty calories. If you consume it at the expense of healthy nutritious meals and beverages it will lead to multiple nutrient deficiencies in the body causing malnutrition and weakness. Dark circles under your eyes suggest poor nutritional status due to dietary deficiencies. You must limit intake of soft drinks by having them once in a week or even less frequently (not more than 200-250 ml of soft drink in a day) if possible and eat a well balanced diet along with nutritious beverages like milk, milkshakes, buttermilk, coconut water etc which will provide vitamins and minerals to make up for the deficiencies. Sleep well at night and stay active during the day. Try to change your eating habits and lifestyle to remain healthy and strong.