Both of those supplements you mentioned contain hyaluronic acid.
http://www.wisegeek.com/what-are-hya...de-effects.htm

Hives is a listed side effect for oral use of this compound.

But one would think they would go away as time passes since you used them.

Many cereals, breads, and pasta products are fortified today, and contain the B vitamins. Not in high amounts however.

I would not really focus on the blood work for the B6... you can look on the net and find many people asking the question about being in the high range for it. This begs the question as to how accurate the range really is. The B12 range which is still used goes way down low to levels (200pg/ml) listed as normal...which will produce neuro symptoms in some people (deficiency). (below 400pg/ml).
So the ranges for other nutrients might also be out of date as well.

Dermagraphia is a common sign of HAE:

http://www.asthmacenter.com/index.ph...nd_angioedema/

This allergy link above explains HAE.

I would look to what you consume daily as food. I gave you the links to histamine foods and releasers. Those can cause itching.
Also MSG in processed foods can be very irritating to some people.

The most common infestation in people today is Candida. You can starve this yeast by not eating alot sugar and carbs. There are tests for it too.

An itchy rash also comes from gluten intolerance and Celiac.
Going gluten free may help you too.