Hi, welcome to HealthcareMagic.
Bengay Cream is meant for topical (skin) use, on intact and non-inflamed skin only. So see if there are any aberrations or inflammation on the skin around the neck, where you have applied, which could be the cause of pain. Bengay cream doesn’t contain any active ingredient that would cause pain on application, even if expired. However, I would recommend you to use only products within the date of expiry, and consult a physician/dermatologist
if the pain persists.