Yes, could be a herx...but also could be something else.
Rain = increase in mold in the air. Could be a fungal issue...either allergy or infection. Are you taking anything to combat systemic yeast?
Also, if the air pressure chages, that can affect the balance of water inside vs. outside of cells, leading to changes in symptoms.
Chronic Lyme Disease, Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication/Chemical Allergies & Intolerances, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD ("Secondary Lupus-Like Syndrome"), Osteoporosis, Pancytopenia, chronic malabsorption/malnutrition, etc.; G-Tube; Currently TPN-dependent.
Meds: Zofran, Pulmicort, Heparin (to flush PICC line), Claritin, Colloidal Silver (used topically), IV Milk Thistle, probiotics.