How frustrating for you!!
Charlotte was like that....dream baby, until about the same age.
It could be teeth, but I think you may find it is a growth spurt. She will be going through some major changes about now, and it will mess with her sleeping and feeding. I didn't express but I do BF, and feeding was the only way I could get Charlotte to sleep until about 6-7months when I began to put to bed awake. Even now she still will eat dinner, feed properly and go to bed fine, wake 15 mins later and need to be fed again before going down for the night.

I really hope it is just a phase! In a couple of weeks she will likely go back to Content Olive, in the mean time you may need to try and express a little extra if you can and keep your supply up, just in case. (nothing worse than expressing a bottle at 2am!!)

HTH and good luck, hopefully some of the girls who used EBM full time can give you some more specific advice.