Read this article today that having more sex overall throughout the month increases your chances of getting pregnant because it decreases the amount of antibodies that normally fight off sperm.

"Sexually active women had higher levels of the antibody IgG, common in blood. On the other hand levels of IgA, a different antibody the authors describe as the body's “first line of defense against invaders,” were lower among those having sex most often."

http://www.iflscience.com/health-and-medicine/more-sex-gets-you-pregnant