Man, those itches are a nightmare! I can't think of anything worse that I've ever been through! Even natural childbirth 6 times isn't that bad! But seriously, I'd either stop taking the vitamins for a bit and see if it clears up. Then add them back, but less, and see what happens. If it doesn't clear up after a few days off them, I'd see a dr. We shouldn't try to self-diagnose yeast.

Good luck!