Ionesmum, don't worry too much about the charts - DS was born on the 75th and steadily followed that until about four months (when HV started asking me what food he was eating...ffs! She was amazed I wasn't giving him food till he was six months old, despite knowing what the WHO recommended and kept hassling me until he was six months - saying "Why don't you just try some vegetable purees, don't give fruit or he'll never eat veg - wtf?!). He gained really well on breastmilk to begin with and put on 3lbs in six weeks - then he started getting 'active' and burnt up what he took on board.
I had him weighed when he was 43 weeks old and he was 19lbs. I had him weighed on Wednesday (52 weeks old) and he was 19lb 7oz. He eats lots each day, breastfeeds well and is now following a line just above the 9th centile. I didn't hang about to talk to a HV on Wednesday...
He's extremely happy, healthy, eats a wide variety of food, is growing out of his clothes, learning new things and he was ten days overdue and I had query gestational diabetes, so I wasn't surprised he has "dropped" through the centiles.
I would second the advice about getting DH to settle your DD - it's FAR too tempting to do the sure-fire 'you will go back to sleep if I stick my boob in your mouth' thing - I know, I've done it! I'm sure if she has less milk during the night, she'll want more food during the day.
It does not have to be the end of breastfeeding, far from it. And I would also second the advice about avoiding HVs