I'm so sorry, Lisa. I understand how you feel. I learned from watching my sister suffer from scarlet fever that strep is scary stuff. When my kids have sore throats, I always take them in for a strep test. My kids even get strep WITHOUT a fever. I can't assume that a sore throat isn't strep because of what my kids experience.
I think that MAYBE the doctor says 48 hours in order for the strep to "grow" enough to show up on the quick strep test. Otherwise, you might have to wait for a culture, and I think that takes 48 hours. Last time my son had strep, (and he's a college student) it didn't show up the first time they tested him. It either wasn't strong enough yet, or they should have actually cultured it. His stomach kept bothering him, so I took him back and between the sore throat and stomach trouble issue that didn't go away, the doctor checked again, and there it was.
So, the answer to your question is that any time they get a sore throat, fever or not, I have them checked for strep. I'm uncannily right about it. I'm pushy about getting the testing because of my sister's misdiagnosis and consequent scarlet fever (which was just awful!)
Hope your little guy feels better very soon!
Dawn