i dont cum when i masturbate :/

hi, stop worrying as u r fine
do u stimulate your clitoris because that is where your orgasm will come from
next is your G-spot, this is a para urethral gland which is the female version of a prostate gland, which means it is inside your vagina at the top directly under your urethra. 70% will be up front under the urethra opening and a few in middle and rest in back and few can't seem to be found. now u should be able to feel it like a slight bump and it may make u feel like u need to pee, don't worry; stroke it firmly enough to feel the sensation and do the same with your clit and u will orgasm.
now OBVIOUSLY there is more to sex, u have a mate naked with full body contact and sensations and penetration etc but it helps if u can show mate exactly what turns u on.
good luck and use lots of lubricant