What Is The Cause And Treatment For Fever In An Infant?

My 8 month old has been sick for two weeks. It started with an out of nowhere fever with no other sx s other than being feverish and not wanting to really eat for about 24 hours. His temp went up to 102. Then he started feeling better and a week later his head was really congested and eyes puffy with dark circles. Finally on sunday night his nose started to drain a sort of yellow/green color mucous. We have done saline spray with aspirator, humidifier, hot shower and his sx s are still not relieved. I must add that prior to his fever we were on the road for two days driving to colorado, which is part of the reason we didn t go to doc. Motrin seemed to break the fever. In addition he had gray poop on saturday and today. The other times it was normal.