The causes of recurrent fever in children aged three weeks are mainly due to the following conditions: firstly, it is caused by children suffering from immunodeficiency diseases. If children have immunodeficiency and thus their resistance is very weak, it will easily lead to the invasion of various pathogenic bacteria, which will lead to fever in children after they invade their bodies. In this case, it is necessary to give the child timely immunity regulation treatment, such as the application of gammaglobulin or the application of astragalus oral solution for children. When the immune deficiency of the child is corrected, the child’s recurrent fever symptoms can be improved naturally. Secondly, if there is chronic inflammation in the child’s body, such as inflammation of the tonsils or inflammation of the sinuses, this can also cause recurrent fever. In this case, it is necessary to apply the full course and amount of antibacterial drugs in a timely manner, otherwise it will lead to recurrent fever in children all the time.