Vag tighter than usual

Okay so I'm not concerned, I'm just curious if anyone else has any idea what's going on or has experienced this. I'm on day 5 of my period and for the past couple days I've realized (because I use the cup) that my vag is a lot tighter, almost swollen like. It doesn't hurt or itch, no infection or anything. Just when I feel inside it feels much harder along the walls and the cup is harder than usual to get it. Any idea why?