Allergic reaction to B complex injection?

I'm on a medically supervised diet right now, and each week when I go in for my appointment the doctor gives me a B12 injection for energy. Last week at my appointment, I mentioned that my energy had been really low even with the B12. So my doctor suggested that I try a B complex injection instead. Well, about two hours after I got home that night, I noticed a little redness on the side of my breast - right along the edge of my bra. I figured the bra was irritating my skin, or that it might be a little bit of a heat rash (I live in Phoenix - it's SO hot here). I spent all weekend wearing light cotton t-shirts and no bra, so that I could give the skin a chance to air out and heal a bit. The only problem was that it got worse and worse over the weekend. It went from a little redness to patchy red bumps, and tiny whitehead looking things all over the side of my breast. By Tuesday it was all over the sides of both breasts and starting to show up on my upper abdomen. Wednesday it started itching like mad (I haven't been scratching). Now it's Thursday and it's all over my breasts, my abdomen and now on my back and I'm unbelievably itchy. I tried using an antihistamine - oral and topical - but it didn't do any good. I've never had an allergic reaction to anything in my life, but from what I've read if I'm allergic to anything in the B complex injection, it could cause this type of reaction. Is that accurate? Nothing else in my lifestyle has changed - no new foods, laundry detergents, lotions, etc. - and since it started right after the B complex injection, I think that must be what's causing this. My question is, when I see the doctor tonight will she be able to give me anything to make this go away, or is it just going to have to work itself out of my system? What can I do to get rid of the itch