Dear Welcome to HCM We understand your concerns I went through your details. Masturbation thrice in a week is not at all unhealthy and depending on your age and other medical conditions, even once per day is healthy. Back pain could be due to the strain you are exerting on your back during masturbation. Alter your position and way of masturbation. Sperm and semen contains mostly fructose, amino acids, citric acid, phosphorus, potassium, and hormones known as prostaglandins. Swallowing semen is not unhealthy but is considered weird and unnatural. Avoid it. If you require more of my help in this aspect, please use this URL. http://goo.gl/aYW2pR. Make sure that you include every minute details possible. Hope this answers your query. Available for further clarifications. Good luck.