The general rule of thumb is chemotherapy is still active in your body for approximately 72 hours after being administered. During this period your bodily fluids (urine, semen, sweat, vaginal discharge) are cytotoxic. It is best to avoid having sex during this period, but for those on long term chemo, such as oral chemo, using a condom will protect your partner from being exposed to the chemotherapy agents that could be present in the vagina or semen.
It is still possible to get pregnant while having chemo, but chemo can cause defects the fetus so it best to always use a condom while having treatment in addition to any other contraception you may be using.
Chemotherapy can affect your white cells and red blood cells. The point of when this is the lowest is called the nadir period. During the nadir period, you are more at risk of bleeding and developing infections. It is best to avoid all sexual intercourse during this period due to the increased risk of bleeding, bruising and getting an infection.
If you feel uncomfortable talking to your doctor about sex, ask to speak to your clinical nurse specialist, or someone else you feel more comfortable opening up to.