There's already been great advice given, and I wish I had a magic answer, but I don't. The 4 - 6 month mark for us was really hard, and apparently around 4 months it's very common for bubs to go through sleep regression. It does pass though, maybe not straight away, but it will all calm down again. We let our DD completely lead the way, have never had a set routine, and it just fell into place a few weeks ago. It takes alot of patience and lack of sleep in some cases though, I struggled too. I found The No Cry Sleep Solution a great book for some tips and pointers, but alot of the time it was simply cuddles and BF that worked, and I love the way that book says that's okay too.
Congrats on keeping up the breastfeeding - it sounds like you've gone through alot so you've done really well there. With your bub unsettled at the moment her main point of comfort and security will be at your breast, so if you feel you can keep going through the rough patch it really could be the best move you could make. Your milk is the one comforting constant at the moment for her, when this wide new world is spinning her out a bit.
It does get easier, it's just sometimes hard to see that when the here and now can be so tough