What are the effects for both men and women for having sex while on her period? Are there any infections that could be caused, will the flow increase afterwards?

There . There are no bad effects that will be caused. It is safe. Some women and men prefer not to due to personal preference, and some women prefer not to due to personal discomfort such as cramping during their period, but no harm will be done by having sex whle the woman is on her period.