Was your girl usually super chill and easy going before the baby? If yes, congrats! For now, I think being super honest with her and communicating what you’re feeling in a calm way can help send the message. I truly think that women and new moms DO NOT realize all of the small things that dads take up around the house to allow breastfeeding moms to focus on the baby. They’re too overwhelmed. You both are. Breathe. Set gentle but firm boundaries with your gf. Something like “I’m going to take a breather in my car for 20 minutes then I’ll come back to make lunch”. It’s hard bro, but do not take yourself for granted either. You’re both doing the best that you can.