hiya
Firstly - HUGS!!!
Secondly - sounds like you are doing a GREAT job with her, I mean it.
Both my first and second kids were the same. Some kids are not good sleepers at that age, compounded by coffee groups/friends/your mothers children who had angelic babies that had day naps of 2-3 hrs at a time :roll:
You need to get some sleep, so find someone who can take over for you while you have a good nap. If you don't have family or a friend that can do that, ask your plunket if there is a parent centre near you as a friend went to one and they looked after her baby while she had a sleep. When you have some sleep you really can cope with anything, so what screams at me from your post is that you are really really tired and need a break.
I recommend getting a frontpack or an ergo, so you can be handsfree while baby chooses to sleep on you, as a backup plan for sanity when nothing else worked, and you are sick of putting them down for the millionth time. It got me through for all three kids. The other thing that I made sure I had for my third child after the madness that was 3 min naps of my second child was a rocking cradle or some way to rock baby to sleep. I think the other thing I recommend is throwing away your watch or clock so that you stop checking feed times/ length of nap and just roll with it - it sounds dumb but it honestly made a big difference with my first boy.
Yay you for breastfeeding, it is hard work to begin with but it is well worth it down the track if you are able to keep going with it.