premature ejaculation

Hi guys just joined here.. i hav this one problem while having sex. i tend to cum fast (premature ejaculation ) and it has happened several times. it started two years ago and now its getting to my nerves 

i hav no problem with the errection. when i penetrate i dont last longer than 2minute. however it doesnt take me long to get the errectoon back after cuming but the same thing happens again and  most times i become frustrated.

my girlfriend is getting tired of it and were are starting to hav problems because of this. please help me.