B12 supplement?

Hey there! I’m a vegetarian and have been for almost a decade. I’m chronically deficient in iron and was before I stopped eating meat so I take an iron supplement. I also take prenatal and extra folate because I’m trying to conceive. I was pregnant already this year but miscarried. I mentioned to my OB when I discussed my depression that I worry about being B12 deficient because of my diet. My husband read that it can worsen depression/fatigue symptoms. He prescribed me an antidepressant (which I wanted) but brushed off my concern about b12 because he said my prenatal vitamin should be enough. Can anyone give me insight on this?