My brother developed serious tonsilitis which persisted for over two years from around the age of 9. He became tired, listless and overweight. Before that he was a bright boy and passed the exam to go from state primary to a private prep school. Because of the illness, he missed loads of schooling and was always having to catch up with his class which was a struggle.
My parents' GP was very understanding and referred him to an NHS ENT consultant. It was many weeks of waiting for this appointment during which the consultant barely looked at him, asked about his time off school and said this wasn't enough to warrant taking out his tonsils.
Back at the GP's she sighed and said she disagreed with the consutant's opinion but then explained the NHS had set itself against taking out tonsils (as they have with circumcision!) They would only perform surgery in the most extreme situations after a long period of suffering. My parents only option was to pay and go privately for this operation. This they did and after a much shorter wait, were seen by an eminent surgeon. Before he even examined my brother he brusquely warned that he didn't take tonsils out on a whim to oblige parents who thought it the fashionable thing to do. He preferred to devote his skills to more life threatening throat surgery.
On examination, which was only a second or so, he turned to my parents and said firmly: "This boy needs to have his tonsils out! It's one of the worst cases I've seen!" End of appointment, even shorter than the NHS.
The surgery was performed a week later. My brother was eleven. All went well until a week later when he had a serious haemorrhage. This cleared up until another week later when he haemorrhaged again and had to be rushed into hospital and have a transfusion. He survived this frightening experience after which he never looked back. He lost his puppy fat, grew and regained his energy and did well at school and university with no more tonsil trouble ever. He is now in his forties, 6pt 4in and managing a public company.
Sorry for this long tale Fran but it makes two points.
If you've been offered surgery, go for it, your son's condition must be bad enough to need it. They don't take out tonsils otherwise.
The longer you leave it the worse it can be. Ask anyone who has had an adult tonsillectomy. Your son is only 4 and although it won't be a happy experience it will be a lot less severe than it was for my brother. Good luck!