Iron tablet question- pregnancy

Cut a long story short

: I've been on iron tablets now for a month, as I had a blood test which showed I was slightly anaemic. I've rang the doctors today because I only have one tablet left and they said my iron tablets are not on repeat, If I want more.. to write down what they are with my name and date of birth and give it in to the receptionist.

How the heck do I know i need more?? Do I need to be taking them throughout my pregnancy? Or no? Should I ask for a blood test to check again?