Ejaculation problem while having sex

I am 24 years old male and I am writing this message to get some advice and recommendations from anybody who is willing to help. Since I started having sex with my wife years I was never had any problem of ejaculating. However, These days I began to ejaculate too soon before it gets in a satisfaction stage. Some times it only takes in matter of seconds. I did not use any medication whatsoever nor I use any type of drug. I am not stressed or depressed. so does anyone know what is the cause of this problem? Or how I can get back to my normal ejaculating.