My 10 week old baby girl has started to refuse ...

My 10 week old baby girl has started to refuse the breast in the afternoons and evenings. She is obviously hungry, trying to chew/suck on anything she can find except her dummy or my breast. She is just screaming at the breast, and won't close her mouth around the nipple, let alone start to suck. The only way I can calm her screaming is to give her some expressed milk in a bottle. She takes the bottle immediately it is offered. So far I have been lucky in that I have had some stored milk to give her, but this is running out, and I have not been able to express enough to replace what she is taking from the bottle. She has been diagnosed with reflux, and had been on mylanta, though with decreasing effectiveness, so has just been switched to gaviscon. I have spoken to the child health nurse, and all she could say was to just keep trying. I am wanting to keep breastfeeding, but can't cope with the hours of screaming when she won't attach. I am worried about introducing a supplementary formula feed, as my eldest refused to take anything from a bottle after I had put formula rather than expressed milk into it. Any suggestions would be greatly appreciated.