About three weeks ago I started going to accelerated summer school, and on the second day my face started swelling up. First with my eyes getting really puffy, and then my face becoming red, and then ...
I have heard of people being allergic to caffeine.
yeah, of course lol.
You may be allergic to an ingredient in the soda. Do you get this reaction to all soda or just one kind? Compare ingredient labels. What is common to all the sodas that make you itch or what is different if it is only one kind of soda. You may be able to pinpoint the cause yourself.
If not, go to a medical doctor who has training in allergies. There is no scientific proof that muscle testing actually works.
Very possible you are allergic to something in it. Go to a Homeopath and get muscle testing to find out your allergies, it is painless unlike the usual allergy tests.