I think there's a little more to this than meets the eye. I don't ever recall anyone posting about the itchies and indicating their whole body was affected. I'm wondering if you are experiencing an allergic reaction.
Try to look at everything you are taking to determine if anything else could be the culprit. Especially look at anything new you started taking around the same time. This is not a positive thing and I would probably reconsider taking this if your analysis points to the biotin as the reason for your all-over-the-body itching and the potential to break out in hives. Once the symptoms have subsided consider taking much lower doses to see what's your tolerance level.
What else are you taking and how much biotin, if any, do they contain? Then add up your total biotin consumption, because it's quite possible that you are consuming much more than you think.
Good luck.