Hey Casey, glad you found your way back.
As you acknowledged, we have to quit for ourselves. I am in my late 20's as well with two very young kids and a wife. When I found KTC and quit 3.5 years ago, I came to the same realization you did. While it seems like there would a greater chance of success if we quit for our loved ones, the one constant in life is ourselves. Heaven forbid something happens to our loved ones and we attached our quit to them. Then what is to keep us quit if they no longer are in our lives? We've seen it many times here where someone quits for their wife or girlfriend. But then after the divorce or break up they are right back to sucking on a dead weed in a plastic can because they never quit for themselves.
I personally never experienced the level of withdrawal symptoms you describe but I'm sure there are many people here who have. I would echo RDB's recommendations and maybe suggest also drinking cranberry juice and integrate an exercise routine. Ultimately, it may come down to will power to push through the migraines and numbness but it will get better if you stick with it.
It's great your girlfriend is supporting you but if she has never been an addict, do not expect her to understand what you are going through. My wife had/has no clue what fighting an addiction is like and I hope she never finds out. But often times, especially early on in your quit when you are experiencing irrational anger and/or impatience, come in here and vent to us since we know exactly what you are experiencing and know how to help.
Finally, when you are craving and need a distraction, come in here and read everything you can. Read my HOF speech (linked in my signature); read everyone's HOF speeches. Read people's introductions and stay close to this site. And most importantly, post your promise early every damn day and keep your word.
You can do this.