So it sounds like you’re reacting to the supplements. Find another neurologist. You’ll likely have a long wait as a new patient so call ASAP to get an appointment scheduled. If another neurologist bought your neurologist’s practice, you can probably see that neurologist the fastest.

Did you have the symptoms before taking the B12 supplement? If so, maybe other supplements are also bothering you.

I can see where really strong pins and needles might also be interpreted as hot and cold sensations.

Be sure to get your thyroid checked (TSH is the most important test - only one needed really) as hypothyroidism can cause you to feel really cold and tired along with a LOT of other symptoms including neurological ones. It’s a simple blood test.

When I was 30 I had the Epstein Barr Virus (often leads to mono) and the intense fatigue (and other issues) dragged on for 3 years but as it turned out hypothyroidism was part of the problem. Once I was treated for hypothyroidism I felt a lot better.

Hypothyroidism is very common and easily treated. If you have mononucleosis, the doctors may assume all your symptoms are from that when that may only be part of your story. I feel for you.