Hi, I Have A Question, My Son Is 3yrs Old

Hi, I have a question, My son is 3yrs old and 45 pounds, He has had a fever for 2 days now up to 102 now and vomited twice since last night. He is now complaining that his legs hurt. I took him to the Dr. this morning and they gave me amoxicillan antibiotic and cough medicine even tho he has no cough. They did a strep throat culture but said it was negative. No ear infx, congestion, nothing else. Should I be worried. My mom is with him now while I'm at work & she's nervous...