If you do not have a period and you have back pain and breast swelling, you should first rule out the possibility of pregnancy. This is because after pregnancy, the hormone level in the body increases, which can cause swelling and pain in the breasts. If the uterus increases in size after pregnancy, there will be a painful pulling, which will cause back pain. Therefore, it is recommended to test with early pregnancy test paper. If the test is negative, it is often caused by endocrine disorders, such as high estrogen production and low progesterone production, which can lead to delayed menstruation. This can also be caused if you have ever taken the short-acting contraceptive pill orally, which is a combination of estrogen and progestin and can cause breast pain and back pain, while causing delayed menstruation.