The entry of semen into the vagina does not usually cause pain. Under normal circumstances, semen ejaculation into the vagina does not produce any significant sensation. If there is pain after semen enters the vagina, you may need to consider inflammation or lesions of the cervix, and possibly allergy to semen that may cause discomfort. If you are allergic to semen, it is recommended to use condoms for sex to avoid semen entering your body; if the pain is caused by diseases such as cervical inflammation, it is recommended to go to the hospital for relevant examination and treatment in time.