Will frequent blood tests cause low ferritin levels?

Hi doctor,

I want to ask you something about my blood test results. I did my blood testing four times this month. First time I did my beta HCG because my period was late. Then three days later, I had blood drawn for T3 and T4 testing because I have hypothyroidism. Then 15 days later, I had a test for STDs (HIV, syphilis, hepatitis C, and B) as a yearly preventive measure, and last time I was tested by my GP because I was feeling very weak for nearly a month. All test results were good.

I am not pregnant, and my T3 and T4 levels are normal. I do not have any STD, and my results from GP are all good except for my ferritin level. She measured erythrocytes, leukocytes, hemoglobin, HCT, thrombocytes, glucose, creatinine, ALB, AST, Fe, Ca, Na, K, CRP, and vitamin B12. All are normal, just ferritin was lower than normal (8 µg/L). I am quite pale and often fatigue. My blood pressure is about 100/62 and my pulse rate 90-100 bpm. She said my condition would be due to low ferritin level and prescribed Hemoplus. But I was paranoid if the only ferritin can cause such problems, so I started searching on the internet and read that low ferritin may be due to frequent blood drawing or donated blood. Could that be my case if they took a common blood sample? I mean, I do not know how much ml they take a blood sample and how many blood samples they had taken. Could my condition be really because of my low ferritin?