Exclusive pumping nighttime

So I'm about 4 weeks pp and have switched to exclusive pumping 2 days ago. I'm still struggling to pump and bottle feed the LO as it usually falls at the same time. My other struggle is at night the LO is just starting to sleep longer so I feel like I want to sleep longer with her but at about 3 hours my breasts become so painful I am unsure if I should get up and pump. I've already had mastitis and don't want to get that again. How do you push you body to get used to sleeping a little longer without the engorgement when EPing?