Amen, and YES to everything HealthyBratt said. I too used to have chronic drainage and sinus infections till I got off dairy (milk is a mucous-maker; you certainly don't need more of that while you have a sinus infection!) But the reason I am so sensitive to dairy is because of an ongoing problem with candida, which produced a leaky gut, which resulted in milk sensitivities.
As for what you can do right now, I agree that you should get the Xclear. It is far better than just saline, though it does have some saline in it. It also has xylitol and GSE (grapefruit seed extract), which is antibacterial and antifungal. And definitely do the garlic. Garlic is antibacterial, antifungal and antiviral. Don't waste time with garlic pills; fresh garlic is far more potent. He can have it in the form of goot applied inside and outside the nose, or garlic poultices. To get it in him, make garlic tea (one crushed garlic clove in as much water as you want to swallow, sweetened with a little honey--for kids and husbands with an aversion to garlic, I use about a tablespoon or two of water. It's more concentrated, but they are done in one swallow.)
Last fall a year ago I had a sinus infection that lasted seven months. The first symptom was a very tender spot on the bridge of my nose. It felt like a bruise, but there was no discoloration. I went to the doc and got put on antibiotics. Then the heavy drainage started. I couldn't breathe through my nose at all and felt like I was choking on the drainage in my throat. Five rounds of antibiotics later, I still had it and just as bad. I decided to stop the antibiotics--they weren't helping, and I felt they were probably wreaking havoc with my gut, kidneys and liver. But what to do? That's when I read Rebekah Anast's (Beeyoutiful Girl) article in No Greater Joy on how to make garlic tea. I didn't think it would cure me, but I hoped it might help me feel better, at least till I figured out what else to try. I drank the first dose in the morning and by the end of the day, I felt better. By the third day, I could breathe through my nose some of the time. By the seventh day I was symptom free. I kept taking it for another week though, since I had the infection sooo long. I wanted to make sure it was really gone. And it was! And that was only with garlic tea. I didn't even know about Xclear or goot back then!
I hope your little one will be feeling much better soon. We will be praying for him, and you too.