Medicine Allergy

Patient: My Dr. prescribed ativan (2mg) to help me sleep. i deleloped an allergic reaction, with itching, rash, etc. after taking 2 doses. Now he has prescribed valium (2mg) to replace the Ativan. I looked Valium up and it is the class drug as Ativan. My question is, if I am allergic to Ativan, won’t I be allergic to Valium?Thank you.