Questions about teething?

My son is 13 months old and has 6 teeth, he hasn't gotten a new tooth in about 3.5-4 months. A couple months ago he had symptoms of teething (fussiness, chewing on everything, drooling, pulling on his ear) but nothing popped through. Then he stopped having symptoms. And now he's having symptoms again and still no new teeth! Is this normal? Does teething always involve cutting a tooth, or can he just feel it under his gums and then it stops for a while?