Have you tried any homeopathic remedies? Hyland's Teething Tablets work well for some. Giving Chamomile can also be very helpful. (It will calm him down and help him rest.) Sometimes, when they're so irritable, and you've tried everything else, then Tylenol (or later on Infant Motrin) turns out to be the way to go (speaking from experience, with a 12 mo daughter who has been working on at least 2 of her molars for the past month, and neither has broken the surface yet!). I avoid OTCs in favor of homeopathic solutions as much as possible ... it tends to be much safer.
Other products: Boiron Homeopathic Medicine Camillia Teething Relief, Hyland's Teething Gel, Hyland's Calms Forte For Kids, Hyland's Chamomile 30x Tablets (a tablet version of chamomile!!)
And when he actually begins to cut those teeth, you may want to consider Baby Orajel applied MINIMALLY to the exact area where those teeth are popping through.