this is called premature ejaculation,thats nothing to worry about
the best way is to deviate your self from your mind as its all about self control,
do like this,if you cum in 3-5 mins,have sex for 2-3 mins,when you feel like cumming stop the penetration play with your partner,stimulate her clitoris ,make love to her for about 5 mins,and then start again,and repeat this until you have maximum pleasure,
trust me on this mate..the final orgasm would be worth all the bust stalls you've stopped.
you can tell her to give you a blowie and then once you come you start over agin after a while.
or try to masturbate 2-3 hours before having sex,that helps you abit,,
and reduce masturbating other times coz frequent masturbating causes premature ejaculation,but personally for me i dont like masturbating atall,coz when you have someone to do it,why do it yourself?
the main reason to have sex is to make love and feel pleasure,
you can try delay creams or sprays which would do the trick but it cuts the feel of sex,,once you use them you wont feel your cock for a while,which actually paralyses the skin of your penis that instance,so no pleasure whatsoever mate,,do you want to be a pornstar who can last long and bang the hell out of the chich or be a gentle lover who can have mutual sensual orgasms
if none of this helps you,,use delayed condoms liek durex performa/performax
or if your a lil bit tight on your wallet you can try stamina condoms which would do the trick,yet you might feel abit unsatisfied though you can last long,
or you can try having a beer or a few shots,
feel sex,dont do anything to kill it!
its all about practice mate..and when time goes on,youll get over with it,
good luck!
cheers