Anemia, anxiety, and doubt

I take iron supplements, because I've noticed that when I take them, certain symptoms I have go away, and when I stop taking them, after about two weeks, they come back.

Last evening, walking anywhere was physically painful. Today, I felt out of breath all day, eating was difficult and unsatisfying, and in between my classes I passed out on my mod couch for two hours. Then I took an iron pill, and I was able to go to class. Then I took another one when I got to class, and now I feel like a person whose limbs aren't constantly angry at them.

I hadn't been taking my iron pills because I ran out of the slow release kind, and I had my backup bottle of regular ones but if I take those on an empty stomach, they make me throw up. The thing is, I'm not diagnosed with anything related to anemia, so whenever I've been taking them for a long time (same goes for B12) and I run out, part of my brain is like "This is just vitamins. You don't really need these, it's not like a doctor told you to take them."

My trust in my own judgment and self-perception has slowly been improving, but I really feel like what's happening here is that I'm semi-consciously responding to the part of my brain that says "You need these" with "Prove it." 

This pattern results in me, once or twice a year, being physically immobilized because my blood stops working.