Emmecat I would say there's no harm in ringing a few others JIC.  Hopefully the midwife gets back to you soon.  She might have had a busy few days with birthing so hasn't had a chance yet. The first contact is important so perhaps she wants to ring when she can fully focus on you!
When I did my ringing around some of them took 3-4 days to ring me back.  It is frustrating waiting I know!   
There's no harm in arranging to meet a few midwives before you choose one.  Hopefully you get to one you want though 
 
 
I would say ring her again this afternoon if you haven't heard from her.  I'm sure they're used to hormonal pushy preggy ladies  
 
  
 