Like other people suggested that your son may have Ear infection, teething.... if your son has those symtoms..then he should have a fever.. For ear infection, you can notice by looking at him if he 's keeping touching ears, or pull down...And for teething, you can always look up.. As you said, he doesn't teething
For what I've learned that MUSIC can keep him calm down. That why I always put the music on for my 16 months old. For napping, if you let him takes a nap near by the night, then he won't be able to go to have a long sleep (over night).. I'm not so sure if you send him to the daycare ??? it happened to my little one, we sent him out to the daycare, after the 2nd day, he wake up around 10pm (he always goes to bed at 9pm) and screamed , cried... so I had to lay down with him until he fell back sleep...or maybe during the day, he played..and maybe something happened.. He may feels insercure. So just try to calm him down by turning on lullaby music. Hope will work out for him .
Good luck to you