What about Oral/vaginal sex during a woman's period?

What about it? For oral sex, this is a taste/smell issue; some
people like it, some people don't. If both partners have no objections,
go for it! I know women for whom orgasm is a wonderful reliever of cramps.

As for vaginal sex, well, you need less lubricant. It's messy; use
something (perhaps a red towel) to protect the bedsheets. Or do it in
the shower, get clean and dirty at the same time!