I have a rash & welts on my body in many places. i'm being treated w/antibiotics for lyme. how can i tell if rash is allergic reaction or herx word?

Herxheimer Reaction: The most common symptoms reported include increased fatigue, joint or muscle pain, skin rashes, photosensitivity, irritability, paresthesia, dizziness, sleep disturbances, asthenia, muscle cramps, night sweats, hypertension, hypotension, headaches (especially migraines) and swollen glands. From what you describe yo most likely have a drug reaction. A biopsy of the skin can confirm the diagnosis.