Hang in there. I know, lame advice. There isn't much else to say, though. A plus is that even if you feel like you're just going to blow without porn, there hasn't (yet) been any sign that withdrawal symptoms are actually dangerous, like say, detoxing from extreme alcoholism or something. I had some serious pain from "blue balls" and can offer advice on that if need be, but aside from that it is riding it out.
How to avoid the urge and avoid withdrawal symptoms... Triggers, triggers, triggers. Our brain maps out all of the little things and rituals that happen before porn for us. The more you change things up, the better. It takes some practice and work to really figure out your triggers, and many of them hide in plain sight. Some are sexual (thinking about porn during the day, flashbacks, attractive people you saw during the day), some are practical (the evening beer, sitting at the computer checking emails), some are time based (your day off from work, late at night when you can't sleep) and some are psychological/emotional (thinking about an ex, stress about work, family issues). The further you follow the path of triggers the more likely you are to slip into "Zombie Mode", but also the more you'll experience the withdrawals, because so much of addiction is about anticipating.
If/when you relapse, keep the relapse short. Don't binge. Don't give yourself a week or three off from rebooting. That will erase your progress, and perhaps even make things worse. Keep the relapse as short as possible and get on the wagon again, and you'll eventually get strength, bit by bit.