I don't think you should be looking on here for advice about this. If he has a fever that means he has an infection of some kind. The best thing would be have his doctor see him, and ask his doctor for recommendations.
I'm surprised that he's getting a cough suppressant. At least when my kids were little, pediatricans didn't recommend cough suppressants. Instead, they'd recommend expectorants, which are aimed at loosening and bringing up mucous. Lots of times what causes a cough is mucous that drips down the back of the throat. A cool-mist humidifier was always something the doctor would recommend.
I'm assuming you haven't brought him to the doctor, because I'm also assuming that if you did the doctor would have advised you about the dose for a fever reducer for him. I wouldn't fool around with a fever, because if, by any chance, your son has an ear infection the fever could rise really quickly (and it's when a fever rises quickly a child can have a febrile seizure).
With a child as young as two years old, another reason I wouldn't fool around with any kind of cough or other apparent mucous congestion or croupiness is that some infections can go from seeming minor to being serious fairly quickly. If you have brought him to a doctor, call back and ask for the doctor's advice. If you haven't, he'd be better off if you do (and let the doctor tell you it's "nothing" if, in fact, it isn't).
An infection can be the cause of the mucous and the cough. Unless he's bundled up awfully warm, fever is most likely a sign of infection. In any case, I really think you should be asking your pediatrician (or at least the nurse in his/her office) for advice. If he didn't have a fever it might be a different thing, but since he does, I wouldn't fool around with it.