trying not to worry

I've just come back from the kidney specialist. Both kidneys are only functionning at around 30% at the moment; he doesn't know why. He asked me a lot of questions about my medical History, and I've got to get a further blood test, kidney ultrasound and 24 hour urine sample for next week when I go back to him.
I'm trying not to worry though. Dad assures me that it is hopefully just an infection which can be fixed with tablets. -- It's only since 07 when this has happened as the specialist got some blood results from back then and they were totally fine.
He said this could very well be linked to my tiredness; or some of it anyway.
What can I do? I shouldn't worry myself stupid til I get some more results.
Til Next time, RdFreak