Why am I missing periods and feeling low energy?

Chemotherpay drugs cause irregular or temporary stopping of periods. See your gynaecologist

It’s completely normal to feel anxious about this. When you don't get your period after having unprotected sex, it’s usually a cause for concern. Stress, hormonal imbalance, or pregnancy could be delaying it. Also, the fact that you took an emergency contraceptive might mess up your cycle. Just give it some time and you may see your menstrual flow soon. However, if there are other unusual symptoms or the delay persists consider taking a pregnancy test.

If you have taken your Diane 35 pills correctly and consistently as prescribed then chances of becoming pregnant are very low. But if you have missed any pills or taken them late, the risk of pregnancy increases. Just to be sure you can take a pregnancy test. 

Unless your doctor advices otherwise, it’s perfectly safe to have sex when you are pregnant. Your wife’s body is undergoing transformations, but sex will probably not harm the baby. However, in some cases it is necessary to refrain from sex due vaginal bleeding or premature labor and low-lying placenta. Changes may occur such as vaginal dryness, but a water-based lubricant can rectify it. Also, if it’s uncomfortable try different positions. Communication is important, discuss with your doctor and partner.

The pills you swallowed are supposed to terminate the pregnancy; however, this might not happen immediately. Sometimes you may go through cramps, bleed, or even pass out some tissues. It may take some hours or even days for all these to happen. Should it be that you are scared or maybe you are experiencing too much pain or bleeding heavily, please seek medical help as soon as possible. 

15 days delayed periods after unprotected intercourse can be a sign of pregnancy or may be some other health issue. Please talk to your gynecologist