Do you ever notice your vaginal discharge or cervical mucus is different in consistancy and color through-out your monthly cycle? This may be able to help you determine when you are ovulating and at your fertile peak. When your discharge is of the consistency of a raw egg white...sticky, clear and thin, you are at your peak of fertility and ovulating...this is when you want to be having sex.
This is commonly used in natural family planning as a way to know when you are most fertile so that couples can practice abstinence or go full force in planning a family.
Hope this helps plan your next bundle of joy!!