welcome to healthcare magic.
it is very good that you want to lose weight. with long working hours it is not possible to make time for the gym or do some exercise. however you can really keep a check on your diet which will go a long way in helping you lose weight. also if you feel tired n weak then get a complete haemogram blood test
profile. this will basically tell you the cause of you feeling tired and you can take treatment if needed. you can consult a dietician who can plan out a diet for you as per your body's constitution, just remember whatever you do should be slowly so that the body does not suffer.