Alison...I just went yesterday to get my dodgy warbelling checked out by the doc, and to ask for advice....
Told me the choirboy wobble ( voice breaking thing - that I too have) is mostly due to being over tired, and worn out.
Advice, given, no singing for a couple of days (a week) and get lots of sleep...
Seeing as I usually have at least 2 gigs a week, I am going to find that hard... So I asked her if I can book a quiet week next week as this week, I'm too busy...
Hope this insight helps...
Ella