When to time sex?

Princess • I am 28. I have one baby aged 2. TTC baby number 2 and no luck :(
Do i have to have to have sex on the same day of ovulation or the day before? Ttc since 6 months and no luck. I used concieve plus now im using pre seed. I am taking folic acid and agnus cactus. My hubby and i are 28. I have a 2 year old son. I got pregnant easily before. Im worried something is wrong with me. I use ovulation kits too.