How do I measure fat%

I knew I should not have checked!

I'm very sick, with fever and almost unable to eat. I'm bummed I'm ill cuz I'm missing my workout day:( however I did not want to take measurements till may but checked today. Yahoo I lost inches of my legs but getting on the scale my fat % went up! How the heck does that happen? I'm lifting and doing cardio on a reg basis, makes no sence.

Any suggestions on what's goin on? I feel great. Is my calories to high? I'm always under by 300-600