I assume your son is around a year since you haven't mentioned his age.
Your son is likely to be suffering from viral fever
and virals usually subside in 3days.kids during this period can get cranky and loose their appetite.
For fever you can safely give crocin
P .The advantage of giving meftal is the action remains for a 6-8hrs whereas Crocin acts for 4-6hrs.While on these medication you need to keep the child well hydrated.
It can be quite a task taking care of a sick baby but you will have to be patient and give time for the viral to subside.
Giving antibiotic will not solve the problem in fact might generate more side effects.i would suggest you to get in touch with his doctor if he gets dehydrated and if fever does not subside in 3 days.