@kate124 don't be too hard on yourself! You've been doing far more than most! If you eat bread then you'll be getting folate, and from green leafy veg.
I'd be directing my frustration on the FN! At every stage of my fertility journey so far, each person has asked if I been taking folate and vitamins!
Anyway, I agree that not taking vitamins would not have an impact on the HCG level.
Thinking of you, but I'm sure everything is fine!