Hello, The most  probable causes for gaining weight are hypothyroidism,Anaemia. These two cause fluid retention in your body which leads to gaining weight and in turn lead to shortness of breath..So get thyroid,CBP,blood sugars,Vit D3,  and ECG checked and see the doctor. In addition to the medication maintain regular diet and exercise. If you get shortness of breath on walking for a few distance get 2 D echo done. Wish you a healthy life

Most cases of shortness of breath are due to heart or lung conditions. Your heart and lungs are involved in transporting oxygen to your tissues and removing carbon dioxide, and problems with either of these processes affect your breathing. Avoid exposure to pollutants. As much as possible, avoid breathing allergens and environmental toxins. Lose weight if you are overweight. Take care of yourself. If you have an underlying medical condition, take care of it. Have an action plan. Discuss with your doctor what to do if your symptoms become worse. Avoid exertion at elevations higher than 5,000 feet (1,524 meters). consult physician...