Is It Natural To Have A Strong Erection During Masturbation?

hi..I wanted to enquire that is it natural to have a strong erection during masturbation..but during sex erection is not so strong..I have been married since last year dec but our sex life is not so good..We have been satisying ourselves by masturbating each other..and had good sex during beginning..but lately I am not able to satisfy her coz of not so strong erections..