Allergies?

My wonderful, beautiful, Peyton might be allergic to the sun.  If not, she is having the worst reaction to an antibiotic that is making her sensitive to the sun.  This probably wouldn't be so bad if we didn't live in the sunniest state in the country.  It doesn't help when I put sunscreen on her, and the hives that she has are horrible.  How can you tell a 2 year old that she can't go outside?  She doesn't understand that it can make her sick.
Now she has scratched so hard, she has cuts.  I feel for her, but I don't know what to do.