Hi M.M.,
So sorry to hear your little man is going through this. I'm not looking to talk you out of your decision as you'll need to do what works best for your family but after reading your post I can only wonder if you've asked yourself, "WHY, is he always sick?" I encourage you to seek the answer to that question.
Have you entertained the idea of having him seen by a chiropractor, osteopath, homeopath or naturopath? If he's recently been on 3 different antibiotics, his body is possibly in a candida like state and is unable to fight off any illnesses while under such stress. Is he taking a probiotic? Vitamin C and D are excellent for helping to boost the immune system. I would limit or possibly eliminate all added sugars and dairy from his diet as well.
An excellent reference is Smart Medicine for a Healthier Child; by J. Zand, et all. You can google it and search sections in the book to read what it has to offer.
Google Dr. Mendelsohn's book, How to Raise a Healthy Child in Spite of your Doctor as well. He has a section in here on tonsils and adenoids that you may find interesting.
When my daughter had dark circles under her eyes, we were advised to detox her body. We used a nutritional supplement called Cell Food; 5 drops/2x a day in juice or water and we saw huge improvements. Like your son, my daughter was having health issues where her immune system was stressed. We've worked at boosting her immune system by means of a healthy diet(no dairy or added sugars, no processed or preservative laced foods), exercise, staying hydrated and nutritional supplements when needed.
As I mentioned, I'm not looking to talk you out of your decision. You need to do what is best for your family. However, I tend to feel that his adenoids are inflamed due to a response to something going on in the body. Find the reason and work on boosting his body's defenses so that his body can heal itself.
I remember when my oldest had surgery(different issue but still surgery). He was in first grade and I was a nervous wreck. Try to stay calm and know that you are doing what is best for your family.
Peace & Light,
J.