Just a phase?

The last few weeks we've been going through quite a rough patch with Annika.  I'm not sure what has caused the change, but it's like she's a different kid.  She resists going to almost all her activities (school, swimming, soccer, Y Neighbours, children's church, etc), and she's gotten incredibly clingy.  She's always been an introvert, but now she says she doesn't like being around crowds of people (and by a "crowd" she's referring to the 13 other kids in her preschool class :P) and doesn't like being in noisy places.  She doesn't want to be separated from me.  She's acting out quite a bit - having tantrums that could rival any two year old.  Bed times have gotten to be a struggle, with her often getting up multiple times before finally falling asleep.  She complains about her legs hurting, her stomach hurting, her head hurting (usually this happens when she's supposed to be doing something she doesn't want to do).  At bed time she says her legs "feel crazy" and she can't get them to settle down.  She's been wetting the bed almost nightly.  Tonight she told me that she was scared of the dark (something she's never had an issue with in the past).  I have no idea what's going on in my sweet girl - is it growing pains, restless legs syndrome, anxiety about starting kindergarten (could it be starting already?)????  I hope and pray that this is just a phase, but since it's been going on for almost a month, I've made a doctor appointment for her for Thursday just to see if the doctor can shed any light on what's going on.