I say continue the nasal rinse, drink plenty of fluids and see how he is Monday. If no better than a follow up at the doctor would be in order.
I am such a firm believer in building immunities through nutrition and vitamin supplements. I would recommend this to prevent so many colds. I would also wonder whether there is an allergy going on. I live in Dallas too and when the weather changes suddenly like it did today that can kick up the allergies. Building immunities can help stave off allergies too.
Have you switched to non-toxic cleaners in your home. Cleaners can cause allergies as well.
Contact me P., if you are interested. I have my own Shaklee business and I would be happy to make some recommendations for cleaners, vitamins and nutritious shakes.
P.