🙌🙌💭💭Missed period day 3 😱😱😱

We had sex purposely without protection the week showing green including ovulation day. I been taking prenatal vitamins since that week. I am 27 and my husband too, we had our last child #2 eight years ago and we are ready for another one and decided to plan it. However, that same week I saw my OBGYN and she said pregnancy will not happen when I want it to happen 😥 so she now has me really worried 😦 She said you usually get pregnant within 6 months of trying 😟. I have not been in birth control since many years ago maybe when my daughter was 2 I stopped and only use condoms. Now I was expecting my period 3 days ago and yesterday I just had like brownish discharge kind of the kind you get before your period, but today day 3 nothing again very lightly brownish discharge. I took an equate pregnancy test yesterday and it’s negative. My periods are regular and last only 4 days my cycle is usually on day 23. Now my question is do prenatal vitamins mess up your period if not pregnant? I decided not to buy a more expensive pregnancy test because the OBGYN lost my hopes at this time. What you all think?? Any thoughts 💭