I could use some baby advice!

Well, I am loving being a nanny. But the little baby I watch is teething. He is only 4 months, but it's definitely happening. He screams for hours on end, and refuses to fall asleep even though he is so tired! 9 hours of a fussy baby, four days a week is not easy to deal with and I would love some advice! The parents don't want me to give him medicine unless he has a fever, and other than letting him chew on stuff I have no idea what I can do for him. Help!