I am 18 yars old and use to masterbate(about twice or thrice a week) . Is it very harmful?

Is it against your religion?

It doesn't help your real sexual performance very much.

It really depends on in the context in which yo mean this. Frequent orgasm, either by intercourse or masturbation is healthy for the prostate. However, it can be detrimental to a relationship.

Physiologically, that is about the normal to normal low rate for most males. Relationship wise, is case to case. Is this hurting your relationship with your partner?

Religion wise: Depends on your faith. A lot of faiths were canonized when sex and reproduction wasn't really understood. There could be a long theological discussion on self-love, but in the end it comes down to what you think and your relationship with your god(s), your world view, and metaphysical universe as a whole.