What will the dr do to see whats causing anemia?

I have anemia and long story short i am thinking of going to a new dr about this. How would the dr know whats causing it? I took iron supplements and my levels decreased by 10. My aunt was suggesting an iron infusion just to get everything back to normal to see how I am feeling kind of like a faster experiment rather than take this much for a much and blah blah blah. I also have a heart condition complete heart block and which both have some of the same symptoms so i need to rule everything out before getting a pacemaker