After a coeliac screen was done to check if that might be the cause of the recurring low ferritin it showed I had a low IgA. This led to all my immunoglobulin levels being checked and all coming back below range.
IgA 0.20 (0.8 - 4.0 g/L)
IgG 3.65 (5.5 - 16.5 g/L)
IgM 0.24 (0.4 - 2.0 g/L)
I’m not sure how significant the low levels are but My GP is referring me to an Immunologist. Maybe this will provide some answers.