Baby night sweats . Please help

Last night my son came down with small fever. I gave him Motrin and he slept through the night and was acting perfectly fine all day today. We figured maybe he was teething of some sort. It's 2:30am right now and I've gotten up twice because I hear my son's small whimpers. I walked over and his hair and back and shirt are soaking wet. No fever. Very odd. I took his shirt off and put him back down with the fan on, thinking he was hot. Second time I got up he's whimpering again, I walk over and he's covered himself with his blanket and is sweaty again. Temp was 98.9. Gave him some Motrin and he's sleeping..for now... hate not know what is wrong. Does anyone have any comments or suggestions? Please help