L.,
I have tried using Ocean Drops and the nasal aspirator and that helps to clear out what he has in his nasal cavities. Put a drop or two of the Ocean Drops in each nostril and let it sit for a minute to losen up all the dried mucus and such. Then use the nasal aspirator to clean out his nostrils.
Something else to consider is if he has acid reflux. My son has ALWAYS been very congested, breathing very loudly and sneezing a lot. The congestion can develop at any time as an indication of the acid reflux. His Pediatrician was able to link it with several other symptoms and ended up refering us to a ped.gastroenterologist for his GERD, or acid reflux.
Just what I know from my experiences, hope it helps a little...what did your Pediatrician recommend? Your doctor is always there to help and you should never be worried to call him or her about ANYTHING!!! Plus, you're a first time mom and they KNOW you get worried about everything because it is ALL new to you! I do recommend at least calling your Ped... If you're in the market for a new doctor I recommend Dr. Mary Burton off of Hall Rd. and Hyedenreich...she is AMAZING and very personal! We tried a few Peds before I found her!
I know it must have been scary with your son getting the Rotavirus and having that scare of dehydration along with it. My son had Rotavirus when he was only TEN DAYS old!
Good luck! :)