Frequent sex, even on infertile days, increases the chance of pregnancy
Most people understand exposure to disease-causing bacteria, viruses, and other germs causes illness. We know that organ transplants sometimes trigger an immune-system response that might lead to organ rejection. The immune system attacks these "invaders" to destroy their unfamiliar DNA and make you safe again. Most are unaware that the DNA in semen and sperm is also foreign enough to trigger an immune-system attack. The fertilized egg, embryo, and fetus are foreign to the mother’s DNA, too. Recent studies indicate frequent sex, even on infertile days, exposes the woman’s immune system to enough of the man’s DNA that, over the course of time, the female immune system relaxes its attention and doesn’t launch serious attacks against it. This relaxation of immune response makes impregnation and fetal development possible. Most couples are advised to have sex on fertile days but sex even on infertile days or when using in vitro fertilization (IVF) helps set the stage for pregnancy.
One of my BFP tips lol it rings true to me