sleep deprivation

so my daughter is still only sleeping 2-3 hours at night, mostly waking every 2 hours. She also rarely naps during the day. I'm just so exhausted that I can hardly function. The house is a mess, and i hardly ever go out because I'm just too tired. I feel like I'm starting to get depressed and fed up with things. Obviously I love her to bits but I honestly don't know how much more of this I can take. My OH does all he can but he works most days and starts very early. he trys to help by taking care of our older children as much as he can to take the pressure of me but I just feel like i can't do this much longer. My daughter is breastfed and although she will take some formula (usually only about 2oz) she is very picky about when she will drink it. She also wont take a dummy so pretty sure she uses me as a comfort. all this means i can't exactly get help with the night times, although I'm desperately in need of a break from her. I'm wondering if I'm developing some kind of post natal depression? literally some days all i want to do is sit in bed, I'm finding I have no motivation to get anything done or go anywhere 😥