From what you have said, it appears that you are worrying about things that are normal. It is quite common when a person does not have good sex education and not aware of what is normal and abnormal. I can tell you with confidence and evidence that the act of masturbation(behaviour) will not have any impact on your general or sexual health. But, the way you think and feel about the behaviour (e.g. feeling guilty/stressed) can have impacts on health. It is quite normal to have sex once a day and feel sleepy after sex. Sex releases certain chemicals in the body that gives a sense of relaxation (feel happy about it). Ofcourse, if you have sex just before going to office then it is not so good to feel sleepy! Feeling weak is again normal because you can get tired after sex (remember sex involves many muscles and energy). If you have a family history of diabetes and heart attack +/- unhealthy lifestyle (smoking), then having trouble with erection is a warning sign for a master health check-up.

What medicine can be prescribed for a man who is 100% normal? - may be some multivitamins and healthy diet!!