Hello, Period date may alter up to 7 days and it is considered as normal thing. It occurs mostly due to hormonal imbalance & mental stress. Mid cycle blood test is not so important. Breast or nipple tenderness may be associated with premenstrual symptoms. You wait few days to get your period before going to pregnancy test. To maximize the chance of pregnancy, you must do sex close to ovulation time or fertile days. Ovulation occurs 14 days prior to next due date. You can use ovulation prediction kit to predict ovulation in the mid cycle. Here, you may need to undergo some basic investigations of fertility if you repeatedly fail to conceive. You can consult with gynecologist or infertility specialist regarding this. Good luck. For any query, you can directly ask me by viewing my profile.