Does ebv (mono) cause polyclonal gammopathy?

It can but...: Polyclonal gammopathy is an exaggerated immune response which can be triggered by a variety of infections and EBV can be a cause but it's unusual. Even if you have EBV I'd check for other infections like Lyme disease and parasites that could cause EBV to be unusually severe. I advise seeing a good integrative/functional medicine Dr. See https://www.arthritisresearch.us/immune-response/j-kyq.html