Why would my 19month old sons temp. Go from 99-102.8 for 3days all the way down to 95-96? And he now feels cold and clammy but is otherwise normal.?

My son had a fever for three days and a couple of nose bleeds. He has nosebleeds on occasion at night but he had 2 on the second day of his fever and another on the third day. Nose bleeds were atributed to me leaving the a/c on because he was so hot (never sweaty). I was giving him 1.2cc of infant tylanol about every 6-8hrs prn. On his third morning his temp was only 100.2(all temps under arm), at approx 8:30am. His last dose of tylanol had been 1:30am because of discomfort from 102 fever. Throughout the day grandma gave him tylanol every 4hrs on the dot and now about 8-9pm he's energetic, but cold, clammy, and his temp is coming out as 95.6-96.(took it repeatedly to ensure/with same thermometer used all weekend) Should he go to emerg.? Why would he be soo cold now? His temp when healthy and normal is usually 97-98 with the same therm.