Geronimo;
Keep in mind that nicotine is not the only addictive chemical in cigarette smoke. You can up your nic to ultra high levels, and still have withdrawal symptoms. Sometimes you just have to deal with it. If the withdrawal becomes more than you can handle, you might have to smoke an analog occasionally until you can taper off.
I have always used 18mg. In the beginning, I kept a small amount of 36mg on the side. If things got bad, I spiked on the 36, and then went back to the 18. After a couple of months, I found that I didn't need the 36 anymore.
Hang in there, it gets better.