Hi there!
First of all, you are 18 and you have made this decision now to stop porn. You have come to the right place. I am nearly 30 and I have wasted my 20's browsing porn and letting it effect my brain. I'd advise getting as much knowledge as you can on how damaging porn addiction is, because the more knowledge you have, it will serve as a reminder to help you quit. The book, "Your Brain On Porn" by Gary Wilson is a great start.
Also, the more you search the forums, the more different methods you will find from other people about how they quit. It is important to choose a method that is right for you.
The stress you feel when you abstain from porn is part of the process sadly. This is your brain rebooting, and it can be painful but focus on your long term goal and let me tell you, I have used porn since I was 17 without a serious commitment to stop, and the life I have lived with porn is sooooo not worth it, it has diminished my self esteem greatly, never satisfied me sexually, (I'm still a virgin) and I can't fathom the time and money I wasted so just remember stopping porn at 18 gives you your whole 20's to look forward to and you will have an enriched life for staying away from the garbage.
God Bless.