Why is it hard to put a tampon in sometimes?

I ask this because I just had a really hard and unpleasant time putting one in. It's usually so easy this is the only time I've struggled. It's the 3rd day in my period and I'm wondering if there's anything that could be causeing it..... If it helps I was messin around the other day and got pre cum on me down there like the first day of my period and I was just wondering if like pregnancy could have anything to do with that, I know it's a slim chance but I'm just concerned.