Why does it hurt sometimes to have sex after i haven't had sex for about a week (the week is usually when i'm on my period)?

Painful sex: After a week of abstinence, the muscular walls of the vagina are contracted, and intercourse may stretch the opening of the vagina, which causes pain. In addition, there are some infections which cause pain vaginally, so see your healthcare provider to investigate the possible cause, which may be an infection: bacterial or otherwise.

Complex questions: There are multiple causes of intercourse pain. Endometriosis, pelvic adhesions, infection, intestinal issues and poor lubrication are just some. If this is a recurring problem interfering with your ability to have a satisfying sexual life then an evaluation would be warranted.