Do as Paxiled stated! some people do get rash from probiotics.
Yes, of course. It's unlikely to be the D if it's D3 or the B complex, but it could be an additive in the capsule. I don't know that company for the probiotic, but if it includes unproven probiotics that could also be a problem. Not all supplements are created equal, and one of the differences is the fillers and binders used to make the tablet or capsule -- cheap brands use cheaper ones that are more problematic. Stop taking all of the supplements; if the hives go away, you've found your problem. Add them back one at a time -- when the hives reappear, you've found your culprit.