I'm 40, in great shape. I act and have the energy of a 20 year old

At 3 weeks, I was in no shape to do the activities that you are talking about. Stamina was still very low. I could do longer walks, but I would need to rest afterwards. Sitting was like Valerie described.. not comfortable. The donut helped, but I still couldn't sit more then 45 minutes or so at a time, and if sat more then 4 hours in a day, I really felt it.
Your healing could be different, but I would guess closer to the 5-6 week mark, but even at that mark, depending on your surgeon, you should be dilating 3x or more daily which might be difficult, unless you have a break in the middle of your day schedule. I went back to work at 8 weeks, which was ok. But the dilations made it a super long day, but I got by with just two dilations during the week daily, from months 2 - 5.
Do you have the option to do remote classes for weeks 4 and 5? Easing back into your schedule as you feel it?
It would be interesting if someone that did manage to resume normal work/school activities after week 3 could post.. You may indeed be able to, but from just about everyone I know.. 4 weeks post was a minimal.. and even that was tough from the stories I hear.
Good Luck!
Melan