Like Graves, I don't have CF but I did have mono in college during one summer school period. I was completely exhausted (and "yes" I had a really bad sore throat too).
The docs had me quit my part time job and take a leave from school. My mom set up the sun chaise in the family room in front of the TV, filled it with pillows and a quilt, and set up an pitcher filled with ice water next to me.
I thought "wow, this is great! I'll sit here and watch old movies on TV and read books and have a fine old time."
Then I fell asleep for 2 weeks.
Eventually, I woke up enough to enjoy watching the movies, but it took me 6 weeks before I could make it through the day without a nap.
Like Graves says, listen to your body and sleep if you're tired and drink lots of fluids. It's a virus ( <a target=_blank class=ftalternatingbarlinklarge href="http://www.mayoclinic.com/health/mononucleosis/DS00352">http://www.mayoclinic.com/health/mononucleosis/DS00352</a> ) so there's not too much else you can do -- tho' I've read that sometimes now they use Valaciclovir (a drug that wasn't available to me when I had mono) during the acute phase...
Take care