Here are some ideas about the schedule problems at school:
- Make sure the administrators know of your appointment dates in advance.
- Help find other teachers or substitutes to cover any class time you must miss.
- Find other time to make up the 45 minutes that you miss by leaving when students do.
- Ask your doctor about adjusting your treatment schedule slightly so you wouldn't have to leave school so promptly after classes end.
- Talk to the administrators in person to make sure they understand the seriousness of your illness, and that you must get these treatments.
If you're doing these things, I would hope they'll be more accommodating. If not, you might talk to your teacher's union representative about what rights you have.
Juggling your schedule is a problem many of us have faced. Sometimes it's possible to make the necessary adjustments. But when you can't be in two places at once, you have to give priority to your health.