It is important to distinguish between fertilization of the egg and implantation of the embryo. Fertilization is the process in which the sperm fuses with the egg through the union of their nuclei (the location of thegenetic information) to form a zygote that will begin its development and give rise to an embryo. Subsequently, the embryo, already divided into several cells, will implant in the uterine cavity and the pregnancy begins.
Fertilization does not cause discomfort or pain, i.e. there are no symptoms of the union of the egg with the sperm. However, the implantation of the embryo can lead to symptoms such as those we have highlighted above: light, temporary bleeding or spotting, slight discomfort, swelling, increased urination, etc.