sorry you are going through that but I think you just need to be patient... I know easier said than done but babies are all so different so is hard to give an "exact " receipe of what it works
I think during the day try to feed her often at this age
if you are using breast milk try not to drink too much caffeine or chocolate as that is passed into breast milk and can agitate her and make her not sleep
also same goes for cellulite creams who have caffeine in them
take her out for walks in the stroller they usually sleep better this way at this stage
at night established a routine with feeding, bath and then bed time.
make sure she is warm... ( I know many books and doctors are all scared of overheating the child and SID and all of that but the baby also needs "heat ". They need to be wrapped or dressed warmly to sleep better at this age. I am not talking big blankets but I noticed a lot of parents have the tendency to really get the babies naked more or less ..) I was told they need one more layer than us at this age and think about you sleeping with a big comforter...
good luck