Acne or allergies?

I am 29 and have had severe acne for about 2 years now.  I tried Proactive but that made it worse.  I now have rosacea has a result of the Proactive.  I have been seeing a dermatologist and have tried many different medications, face washes and topical creams but the acne still persists.  It is the worst on my face from the nose-line down and on my neck.  It is spreading to my chest and back.  I have been on Accutane now for a month, but have seen no difference in the acne.  My acne itches very badly, and it has me wondering if I have an allergy instead of acne.  I have changed my facewash, makeup, lotion, detergent, and hair products but still see/feel no difference.  I have seen that dairy products and other foods can cause skin allergies.  Will an allergy test determine exactly what I'm allergic to (if I am)?  And can I suddenly develop an allergy in my 20's that I didn't have before?

[loiloi]

Hi. Stick with the Accutane, it takes 16-24 weeks to clear acne. After this, you are likely to be free from acne for a long time. Accutane shrinks the sebaceous glands responsible for acne. These glands grow back very slowly, by which time you are likely to have outgrown your tendancy for acne.
Itchy dry skin is an expected side effect of Accutane. Use a bland cleanser, I highly recommend Physiological gel by La Roche-Posay, available online and in stores.
Don't give up, Accutane is the most effective acne medicine available. 80% of patients experience a long term remission from acne after just one course. 20% warrant a second course.
Eloise.