Patience, babies are more fickle than PMs'ing teenage girls. They're fine one minute and the next nothing is going right. They can be content with how their life is and then they hate everything and want a drastic change.

Let them throw their "tantrum" for a week or so and then try again.

And relax, everyone gets nervous when a baby throws a hunger strike for no obvious reason, just take a step back and if your husbandry is right then resign with the fact that they're just being difficult. It's been three weeks and if she is still doing okay with her weight then don't sweat it too much.

I hope this helps you some. Best of luck