I prefer girls only to answer this question (menstrual cycle help?)?

Okay, I'm just going to dive right in and talk about it. I started my period yesterday and it was a fairly heavy flow. No biggie. Tonight, however, I went to change my tampon and I couldn't get it in. My flow had settled a bit, but usually if it's still a light flow, I can get a tampon in problem. Not this time. So (forgive me) I stuck my finger up there to check to see if there was any blockage; I couldn't find any. So I checked myself out in the mirror and couldn't find any abnormalities. So, what's going on? It's like my shrunk and became a dry, barren landscape (for lack of a better term). (Note: I am a virgin, so not like this is going to hurt my life.)