Hi,
I took the pre-conception ones and am now taking the pregnancy ones. I have to say I did get more headaches at the end of my first trimester which I discovered by chance were down to the vitamins. I took them every other day for a while and this helped and now am able to take them every day. I conceived the month after starting to take the pre-natal vits, so maybe they help!
I suggest either taking them every other day, or changing brand. If you don't get on with them though, just ensure you have a really good diet and eat the right stuff. There are plenty of people who say you don't need them. Good luck x