i think unfortunatley it is normal for them to be like that, i think they can start teething anywhere from 3 months but generally don't get any teeth till around six months. DS was like that for about 2 months, then about a week after he turned 6 months 2 bottom teeth poped through over night. i also think at about 12 weeks its a developmental thing, drooling and everything in the mouth etc.
i wouldn't worry, (unless of course his fever and other symptoms get worse) you can drive yourself crazy worrying about one thing or another.
all the best x