bottle feeding....HELP!

my baby girl was doing very well with bottle feeding up until she was 3 week. All of a sudden she started to refuse it, we've tried many different nipples and bottles but she will not take it. we've tried waiting until shes very hungry so that she has no choice but to take it and still won't work. Dad and big sis also have tried. anyone else having issues or has had issues? my daughter is now 8 weeks and i will be heading back to work in 4 weeks. Any suggestions? tricks?