Have you had the common cold recently, or any other kind of viral illness? Sometimes that will aggravate the facial nerve (cranial nerve #7) and cause it to spasm. Is there any numbness in the face? If so, then the trigeminal nerve (CN5) is implicated.
If this is a new problem, then it's unlikely related to your older injury because CN5 and 7 do not innervate the back; however, they do innervate the neck, so if you have any new soft tissue injuries (like from working out), then that could be a factor. These nerves have autonomic functions including maintaining muscle tone in the face. It sounds like they are still functioning but some kind of tissue compression has caused a disruption, hence the twitch.
I would avoid upper torso workouts at the gym for a while as there may be localized inflammation where these nerves pass. Try neck massages, gentle stretching, and heat therapy to increase blood flow. Since you have already addressed nutrition I think it's more likely that a stiff mucle is to blame.
