Are Hair Vitamins dangerous?

I took a specific brand of hair vitamins twice last year. I had no problem, and my nails grew like crazy.

I re-purchased the vitamins a couple weeks ago. I compared the ingredients of the new bottle to my old bottle, the ingredients and supplement facts were exactly the same.

I took the vitamin two days in a row. I had no problem. I skipped the third day and took it the fourth day. Later that day I got a terrible itch in my head. I washed it and it didn't help. The next day I experienced head and neck pains. My scalp never developed a rash or anything. I saw two doctors and got no explanation or proper diagnosis for my condition. I was told that my scalped looked normal.

Has anyone experienced this before?

Could it be the vitamins even though I had them before?