Ellie is a four month old baby who was born at term by natural delivery after an uncomplicated pregnancy, and is up to date with immunisations. Over the last five days Ellie has been very unsettled towards the end of the day, crying for up to an hour even when being carried. The episodes usually start in the afternoon where she becomes distressed, turns red and draws up her legs. Once the episode subsides she returns to her normal self.
Ellie is exclusively breastfed on demand, has six wet nappies a day and is sleeping well overnight.
What is the most likely diagnosis?