I am experiencing an allergic and severe reaction to acyclovir and Valtrex (valacyclovir) for shingles treatment. How do I treat this at home?

See a dermatologist. It makes no sense to use both Valtrex (valacyclovir) and Acyclovir at the same time. Allergic reaction to either of these is extremely unlikely. See a skin specialist immediatly . The correct diagnosis may be something else.
Antihistamine & call. Severe allergic reactions where there is difficulty breathing, throat swelling or near loss of consciousness are treated with self-injectable Epinephrine (epipen). These are by prescription. For hives, itching and mild swelling without heart or lung symptoms, then an antihistamine such as zyrtec, claritin, benadryl, (diphenhydramine) etc can help relieve the symptoms. If this is a drug allergy, then stop the drug.