Hematologist for sure. I am now in monthly IV replacement ( human ). Had alarming low IGg but High A and normal M. After 6 months I am about to break into the low range of IGg. Have less fog head and energy ( I am dealing with lots of other things too tho’ - am on immune suppressant for RA- but works differently - didn’t cause other.
I felt nothing before - but big fatigue. An immunologist found mine too! Thank god! Best of luck with you!