I can't say why it turned red with lemon juice because I've only used lime and citric myself perhaps someone else can. The reactions you had presuming it was ok could mean it was working on your thyroid if there is an infection there causing the Hashimotos
and the headache and fatigue also can be detoxifying symptoms so you could cut back to reduce these symptoms also you were likely taking more than you could tolerate and perhaps not diluting it enough. I've never heard of lemon juice making it red though.
Perhaps you could contact Global Light about this