Why my kid saying there's something wrong with his spit

[Brian1980P]

My son almost 5. And never had issues eating he would eat all the time saying he's hungry a week ago he was eating popcorn and spit it out after every bite he did it like 5 times and stopped and when dinner came he didn't want to eat his favorite tacos when we cooked tacos he would eat 3 hard shell tacos so I thought he's not hungry the next day it was lunch he didn't want to eat that night he asked for a spoon of peanut butter the next day same thing and the next it seems like a week now and all he's eating is a spoon or 2 of peanut butter and a pudding cup now were asking him to eat even cooking his favorite foods he was a big eater but since that day with the popcorn when we ask him if he's hungry that he needs to eat he keeps saying there's something wrong with my spit I research it and don't see nothing about spit we looked in his mouth throat and its good the Dr's my wife works with said if he has the same energy as before should be fine if he doesn't eat today we will bring him to his Dr has anyone seen this before I have a 21 year old son never seen this