Any advice for me? Ferritin of 9!

Hi,
I just got my latest blood tests back, and my ferritin was 9! a month ago, it was 16, and a month before that, it was 24. Therefore, my GP doesn't want me to start taking iron supplements now, so that i can have a blood test again to see if it really is declining so rapidly. Is it unusual for it to decline like that??? I feel SOOO bad all the time and just want to start taking the iron asap, esp. since it takes a while for the ferritin to go up. My MCH and MCV are a bit low, but Hg and serum iron are fine.
What I don't understand is...what the causes of a low ferritin could be, and whether this is a condition of its own, or if it's usually a symptom of something else? I have a lot of symptoms which suggest hypothyroidism and am seeing an endocrinologist soon, but I'm not sure if these symptoms could all be linked to the low ferritin??? My symptoms are - fatigue (very severe!), always cold, cold hands and feet, basal/morning temp of 35.6-35.8C and average temp in afternoon is 36.4C, hair loss, dizziness, weight gain. These are all typical hypothyroid symptoms, but I suppose the hair loss and fatigue could be due to the ferritin? What about the others??
Thanks! Also, my GP thinks it's better/cheaper to get OTC iron supplements...but all of the ones I've seen are 7-14mg/day doses?!?!
Thanks a lot!