Any tips on period sex?

My current bf is the only guy I've been with who's cool with it and doesn't mind the blood. I've never done it before and just know I need to bring a towel to his place since I may get it soooon. 
Here are some of my concerns:
-smelling different
-coming and the contractions forcing out blood
-making a mess when I'm on top
He works in the medical field and isn't grossed out by the human body, but I don't want to just jump into this. Any tips? Thanks!