Stop baby waking during night

Dawn

So from about 8 weeks my baby has been going down to sleep between 7:30 and 8pm, then not waking for a feed until between 5am-6am (amazing I know)

However, for just under two weeks now she has regressed and is waking up for an extra feed between this, usually around 2am. She's 14 weeks old.

Why is this happening and what can I do to get her back to her long sleeps?

She is breastfed, but gets an 8oz bottle of expressed milk before bed.

Thanks