In your letter there are several problems at once. Problem one: the child does not want to go to school and therefore specifically (or not special) gets sick.
You, as parents, have done a lot to find him quite a good school and teacher, but he still does not want to. This means that he still has problems with the school.
And with them, probably, it is necessary to understand.
A child may have many different feelings associated with school. It can be fears, anxieties, shame, strong emotion. If for some reason the child is not aware of these feelings, then they can go into the body, that is, find their expression, appear through the body symptom.
If he does this with your son, then, indeed, he is physically ill, but simply putting him to bed will not solve the problem. Anyway, it’s worth finding out what feelings and difficulties his school causes.
We need to look for the root cause.
The second problem. Your child starts to manipulate you. You keep track of it, notice.
Often children are manipulated when they cannot get something directly. Your son may not be able to get the necessary help from you, therefore he manipulates.
He seeks attention to himself when you leave him to support him at home, but the problem with the school is still not solved.
Unfortunately, your son can gain a foothold model: It has become difficult – do not walk, run away. Probably, it will still be better if he learns a more adaptive installation: It has become difficult – let’s see together! If you yourself can not figure out what exactly are his difficulties with the school, then you can take him to a child psychologist.
And try to sort things out together.