My 3 1/2 yr old came down with sickness yesterday,?

he had a sore throat and a little coughing followed by a slight fever late last night. Early this morning he had a 101 fever and said his arm and stomach were sore so I took him to a clinic. They tested for strep and flu both were negative. Also checked blood for viral or bacterial infection both were normal. They just gave him a shot to help with the sickness and some antibiotics. He is really tired and still has a sore throat. Could it have been to early to tell if it was the flu?? I guess I'm just another paranoid parent, but I have heard of people going to e. r. to be checked, everything was negative, only to return to be told they had the swine flu.