What Causes Itchy Skin Post Methionne Shot?

Hi, I got a shot that included B 12, methionne, choline and inositol. the injection shot itched at first, then it began to turn red and swell to about the size of a 50 cent piece coin. Now the area is whiter than my natural skin tone. It did hurt for the first two hours, but now the pain is gone. What could be the problem?