Urgent help

Hi. Im newly married and I want some time for pregnancy. I had 28 days cycle most of the time before marriage but now after marriage my two times periods messed up 2 3 days before after of my actual date. I want to know if i do intercourse on my 7th day of period what would be my ovulation day? Do u think 7th day is good for intercourse if i dont want preg? Im talking about unprotected intercourse. No pills etc.

I have checked apps and google but i m not getting exact same date of my ovulation. Please help.

P.S my husband doesn't want to use any protection so ive this option only