They are absolute idiots for treating you this way given you sound an amazing employee and they are lucky to have you. Aside from the human element in treating you like this, in pure business terms they are mad. They risk you leaving altogether and then they are stuck with a vacancy which they will have to spend time and money on filling. And spend time and money on training someone new. Bear this in mind if they continue to be difficult, it is as much in their interests to keep a good member of staff as it is for you to keep your job.
Really glad that drs are being supportive. I think now try and park the work situation and concentrate on you and your son.