Toddler with croup like cough....?

Since Sunday my son has been having a really croupy cough at night and is having a harder time sleeping because of it. It goes away during the day and comes back around 6:30-7. The last two nights he developed a slight fever--99.5 or less (he usually runs around 97.8--like me). The fever and cough have NOT slowed him down in the slightest and his eating and all other patterns are normal as can be (except for sleeping of course--he has started waking up at night from the cough--humidifier is helping but not much). I'm wondering if it's allergies, but there are no other things like phlegm, runny nose, red eyes, sneezing etc. Other than the cough and fever he's normal...anyone else's little one have this? The weather goes from 60-88 everyday--like a normal autumn here....