Masturbation is a normal part of a sex life. It can not have a negative effect on health. Moreover, both sides of our body are not ideally symmetrical and equal. Therefore, it is a normal finding in men that one testicle is bigger than the other or the penis, when erected, is more directed on the left or the right side. This does not create problems in a sexual life with a partner, only that maybe the frequency of sexual intercourse in a relationship might probably lower the need for masturbation. However, at the time being, there is no reason to stop masturbating. Given the data you provided, you might want to reconsider the thought that you have a “lost strength” in erection, because from what you’ve written everything seems to be normal. But, if you feel it really bothers you, you might want to visit your family doctor, who’ll refer you to a urologist, if necessary.