I have not used it but I have similar energy rollercoaster experiences that are sometimes clearly related to the quality of a B-12 bottle I'm taking. I am also incredibly fatigued right now (taking Nature's Way B-12 Infusion, which used to be Enzymatic Therapy). When I get this, where I don't seem to be sick but only exhausted 24/7, I try discarding the current bottle and seeing if a new one helps, since B-12 can get degraded and there is variability in the bottles sometimes it seems. Sometimes that does help, but not always. I've ordered some labs to see if something shows up (thyroid, CBC, cortisol). And I always wonder if it could be allergies, although I don't have any strong allergy symptoms.
The difficulty is how interconnected everything is. B-12 will affect thyroid, estrogen will affect thyroid, etc.
Please post if you sort it out.