I never had this problem with blue top generics. I do hear of some getting it though. I wonder if some are more impure than others or if some are 192 and not 191. I'm curious now.
If it does keep up, your best bet is to inject IM. That's what most of the bro's who get the welts do. I would be concerned though if a product was causing such side effects. Maybe I'm one of the lucky ones. Either way, good luck and I hope the IM method helps out. It seems to help the guys over at SSB and Outlaw.