You can get pregnant on you period bit it is very unlikely and it is not the intercourse during mensuration that causes HIV its having unprotected sex with some who is HIV positive. HIV can be contracted through blood but also through saliva and other bodily fluids that's why it is called an S.T.D
I heard that people shouldn't have sex on their period you can get HIV like that
You can but it depends on how your body is.
Yes it happened to me I had sex the first day of my AF in 2001 and it shut completely off and 2weeks later I had a miscarriage so yes you can get pregnant