When to stop breast feeding?

So my son is only 3 weeks old (No I am not planning on weaning him anytime soon obviously).I love breast feeding my baby but honestly it's so tough because I work and he wants to nurse constantly and then I have to try and find time to pump so he hopefully has enough milk while I'm gone- it's stressful 😣, and I don't want to supplement because his pediatrician said were doing great and I'm producing plenty for him to eat. I just don't want to bf any longer than I have to. So i know we still have a while, but i was wondering when you mommas stopped giving your child breast milk completely? and do they go straight to cows milk after that? thank you!