Thank you for your query.
It is very common for children to go off food or reduce their intake following an infection like the one in your son's case. Offer him food that he likes and you will soon see that he should be his normal self,
is a constant process and children like to bite at hard things while the teeth are coming out. There is nothing to worry on this count.
I hope I have responded to your query to your satisfaction. Feel free to revert back if you need to share any other information or need any clarifications.
Wishing your son all the best.