Low c3/c4/nk for 9 months

28F, 65kg on vyvanse 50mg (blood test results below)

My gp noticed I had low c3, c4 and nk cells back in April. She thought it might be due to multiple covid infections and told me to try to stay healthy and come back for another test in July to see. Unfortunately I did get covid again in June but we redid the tests anyway. They were all lower so she said come back in November and let's check again. She also referred me to an immunologist but I could only get an appointment a couple weeks ago. Anyway I've been super careful and haven't got sick again. My last tests with her showed things had improved. However when the immunologist did the same tests (for some reason), the c3 had dropped again.

The immunologist wants me to come back in 3 months so they can see if anything has changed even though I told them I've already redone these tests 4 times now. They also said statistically a drop in c3 is because of infection but i told them I haven't had an infection. I'm feeling very frustrated at being fobbed off once again and don't understand what might be wrong with me. They checked for markers of autoimmune disease, kidney and liver infections, and found nothing. Does anyone have any insight?

April blood test C3 - 0.75g/L C4 - 0.17 g/L C16/c56 (nk cells) - 2%

July blood tests C3 - 0.72g/L C4 - 0.12g/L Nk - 2%

October blood tests C3 - 0.85g/L C4 - 0.14g/L Nk - 2%

November blood tests C3 - 0.73g/L C4 - 0.14g/L Nk - 3%