Iron supplement dose?

Hello everyone! My doctor recently noticed on my CBC that my hemoglobin was down one point and suggested I start an iron supplement every second day. I picked some up at the pharmacy that contains 150mg of absorbable iron, but this just sounds like too much considering my pre natal also has 27mg of iron in them. I was never told what dose to look for nor did I realize there were different doses to choose from! What did you all take? Any recommendations?