Dave,
Were you not advised to take Iron Pills for two weeks before your surgery? Mine are called Ferro-Sequels. I guess each surgeon is different. At the same time (two weeks prior), I was advised to not take any OTC pain relief, so it was a really rough two weeks. I, too, had blood loss and was given two units of blood.... but I didn't have any bleed through-wound/wise.
I agree with Jo... call your GP or OS. Meanwhile, do you have a BP cuff at home so that you can check your BP?
It it's anemia (there are different types) B12 can help tremendously; but I'm no expert and again encourage you to follow Jo's advice. (She's the BEST!)
Alicia