You've received a lot of good answers so far, and you are already doing a lot to help your little guy! My daughter was sick almost every 3-4 weeks from October to February and it was so frustrating. She was 18-22 months and was 25 pounds. We did the same kinds of things that you did, but also added some homeopathic treatments. Since our son is over 2, there are a number of homeopathic cough remedies that you can try by reputable companies. I couldn't use most of them because my daughter was under 2. Also, we used Hyland's C Plus Cold Care, which can help with runny noses. Also, we used a KingBio (homeopathic) spray for sinuses--it's the same for adults and kids, you just adjust the dosage. The spray tastes like water, so it's easier to give than some of the herbal things. That worked for a few days for us. Ultimately, since the coughing was so bad (and my daughter's congestion wasn't loose enough to come out, as we used saline and suctioned her often!), we called the doctor back. He gave us Tussionex, which is the prescription cough medicine that adults get. It has a stronger antihistamine in it and it did take help a bit. The dosage was very small, like 1-2ml. Trust me, I am very much into natural remedies, but when your toddler is unable to sleep because of coughing, it can really wear you down! And, if you can avoid the antibiotics, but relieve his symptoms, that would be an added bonus. By the way, we did take her to an allergist, and the allergist felt that she did not exhibit characteristics of allergies (food or environmental). She suggested that our daughter was just building her immune system through the unfortunate string of colds/upper respiratory infections. And once winter was over, it was true, she has not been sick! Hopefully you can find out the cause of the issue--whether it's dairy sensitivity, environmental allergies or just something that is too much for his immune system to fight off. Good luck and hope you all gte some sleep!