Well there is no set average because it varies from woman to woman and even from pregnancy to pregnancy.
Some women can start having signs within days of conception while other may not have any signs until their period is missed or even later than that. Then you have to consider some women dont have the nausea or other common signs at all. So depending on signs can be misleading.
Hi. I just noticed that it was about the 6 week mark for me too. I have been getting nauseous, but not throwing up at all. As for headaches, I get them early. And sore breasts early-like a week after conception.