R.L.
You may also want to mention to the doctor that you didn't appreciate the dismissive attitude form the nurse when you called. Remember always trust your instinct. If you feel something is wrong, then get it checked out. If the doctor looks him over and find nothing, then see if they can take some blood and do a CBC. This is a simple test that they should be able to do in the office and get the results fairly quickly. This is what my peds office would do for an unexplained fever that is lasting to long. Even though it's a low grade fever, if it's not going away then something may be wrong.
Hopefully it's nothing, possibly teething or a virus, but it could be a sign of something serious. You can never be too careful! Make sure to keep an eye on how many wet and poopy diapers he has. If you see a decrease in that there may be dehydration, but as long as he has plenty of diaper changes he should be OK. Hope he feels better soon!