There are many reasons for the swelling of the chest on the fifth day after intercourse, and it is not possible to directly determine whether it is the onset of menstruation or pregnancy: 1, there are a variety of situations that can lead to chest swelling, such as the onset of menstruation, and many women will appear before the onset of menstruation, mainly due to the hormone level disorders in the body and the problems caused by the problem. 2, there is also the possibility of pregnancy caused by the implantation of fertilized eggs in the body will produce certain stimulation, resulting in hormonal imbalance in the body, so there may also be chest swelling or bleeding in the pubic area and other conditions. Stimulation, resulting in hormonal imbalance in the body, so there may also be chest swelling or bleeding in the pubic area and other situations, when these problems occur, it is recommended to observe the body’s symptoms, if the swelling and pain is more pronounced, go to the hospital to check some see whether there is a pregnancy, and then come back to the symptomatic adjustment. 3, it may also be caused by other factors and other symptoms, such as endocrine disorders or mammary gland disorders, and so on.