Praise be to Allah.
Many brothers(especially the youth) are facing this problem and are having a hard time trying to stop this addiction. Inshallah this answer is going to help and always ask Allah to help you. I'm not sure if you masturbate after watching porn or you do watch porn, however, this answer is to benefit those that do watch or even don't watch. Also brother, make sure you search your question to see if others haven't asked the same thing, many people before you asked the same question.
Firstly, remember who your god is, remember the punishment that will be on you if you continue to do this sinful act, remember the punishment of the grave, remember that the ALMIGHT ALLAH will forgive those that ask for foregiveness as he is the most gracious and the most merciful.
Let me give you a hadith: Allah is more pleased with the repentance of His servant than if one of you gets up and he finds his camel missing in a waterless desert (and then he accidentally finds it). [Sahih Muslim] Imagine how happy you are when you find your camel in a waterless desert, won't you be very happy? Allah is more happier than that person when his servant repents.
Another hadith: If you were not to commit sins, Allah would have swept you out of existence and would have replaced you by another people who have committed sin, and then asked forgiveness from Allah, and He would have granted them pardon. [Sahih Muslim]
The meanings of these hadiths is that you should ALWAYS REPENT, do tauba and ask for forgiveness. If you do tauba, and then you do this sinful act again, REPENT, if you repent, and you get back to this sinful act, REPENT, ALWAYS REPENT, REPENT, REPENT! You must try and make your iman strong, have faith in Allah, and try to stay away from this. I'm not telling you to go and do this sinful act whenever you want and then you repent, no, you must stay away from this.
Go on this website, and download the program, make sure you don't put the password, as you will know it already, make your parents put the password and tell them to never give it to you, once you download this program, it will filter out porn from the internet. http://www1.k9webprotection.com/
If this answer didn't help you, just tell me what else you need and what can I specifically help you with, however, this answer should inshallah help you. Salaam.