before you give antibiotics???

DS has been having fever on and off since Sunday evening. At the highest it was 38.2, taken under the arm. He has been restless, not drinking his whole feed (I formula feed) and giving me the grossest dipers known to mom (TMI - nice sloppy and stinky, but not slimy or other-than-normal-colour)

His fever breaks when I give him Panado (panadol) and he still sleeps ok. He does seems to be more gassy, but I recon it's because his tummy is upset. He will moan in his sleep and let out some gas and then be fine for a while. But he is not himself.

He has not broken out in anything yet .. measels or what-not. I had him at the GP, but his throat and ears are 100% and she feels nothing wrong with his bowels. As Murphy would have it his temp were 36.7 when she took it

This moring he was still a bit hot, but not so much that I took a temp. And he was pretty restless during the night, also did not drink that much. He is not dehidrated (his skintone is good and his fontanel is not dented in)

SO .... after all that ... how long do you think I should wait this fever out before really getting worried?? I don't want to just give anti-biotics if it's only a flu or some other silly virus, but WHEN do you know this has been going on long enough. When do you act??

Sure it could be teeth, after all he is almost 5 months ... but I'm not noticing any swollen gums. He is chomping on everything and drooling like a hungry dog, but that is nothing new for him.

Any ideas??
TIA