If your menstrual cycle is of 28 days, then 15th day will be the beginning of this week. When this happens an egg erupts from its follicle and it is swept from your ovary into fallopian tube. During the next 24 hours, that egg will be fertilized if one (or more) sperm manages to penetrate it.
You should take calcium rich diet. Low-fat dairy products, dark green vegetables, fortified orange juice and soy products are some of the good sources of calcium. You can include these foods into your diet.