Sex for pregnancy

Hello TTC MOMMIES I OVULATE CD15 it’s been like that for years now. I’ve started ttc since august. I had sex 4DPO and ovulation day and it worked but had a chemical. What days have you been having sex for pregnancy. I be tried peak day only and nothing and last month I tried 5dpo and 2dpo and nothing. If you could only have wax 3 days during fertile week what would they be ???