3 year old son spitting and barely eating

[babyhector]

I am very concerned about my son, about 2 weeks ago he had a throat infection and was treated for it.  Slowly after that he began to spit for no reason and began to spit some of the the food he ate..he would eat and then spit some of the food and then stop eating it.  It has been 3 days now that he eats less and less he will tell me he is hungry yet maybe take a bit and then spit the next.  He tells me that there is something in his cheak yet he has nothing that I can see that bothers him.  He will drink milk and I have been giving him pediasure the weird thing is that he can spit the food he likes yet can eat a chocolate right after that with no problem.  I wonder if this is just a face since I am six months pregnant with a baby girl and he is an only child?  I am taking him to the Doctor but is there someone that can give me some light this I am very worried.