Re: When does this get better?
I know you are exhausted, but your baby's feeding pattern sounds very normal. Except for only being up 3 times at night, which sounds like a dream to me, because my kids woke more like 5-8 times a night when they were that age!
There is no point when "everything" gets better for every mom. Life with a baby is a moving average- you should expect good days and bad days, but overall your baby should get easier and easier as time goes on. I have a feeling that you're in a difficult phase right now because your baby is going through her 6 week growth spurt- it happens around 6 weeks, not at 6 weeks exactly.
I felt that my babies got a lot easier around 3 months, when they suddenly discovered the interesting nature of the world around them. They would spend a few minutes trying to eat their own toes or something, instead of needing to be permanently attached to me. Until that point, I felt like we were in the "4th trimester" of pregnancy- the baby was still so small and so undeveloped that she needed me all the time, literally.
I understand that you want to be there for your kids and your boyfriend, but right now I think they need to turn things around and be there for YOU. Your boyfriend and your 13 year-old need to step up and take responsibility for the house, the meals, and the 3 year-old. You need to be free to get as much sleep as possible, and to master the art of breastfeeding this particular baby. Anyone who thinks a bottle is that answer should get a very cold reception, because that just undermines your confidence.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"