This is my first time breeding mice for bare with me, please.

I have 2 mice that are breeding and I don't know the age of either of them because local pet stores don't keep track of that. I had 6 mice and there was only one female out of all of them, so I put her with a male and I was told to wait 16 days, take the male out, and hope she's pregnant. The first day they were just settling in, but a few hours later the male started to go for her. He tried a lot but she squeaked at him and he backed off. I read that she squeaks because she's in heat but she's not ready. But he toned it down the second day, but still tried. She still resisted. But I noticed that in their small igloo, I think it's the girl that's kicking up aspen bedding to make a deeper hole and bringing some back in. They both sleep in there now but I was wondering if that was nesting or just mice burrowing because they want to hide.

Anyway, it's the third day and they're both usually in the igloo, curled up together. And they'll occasionally come out for food, water, and to run on the wheel. But I picked up the igloo because I was curious about why they dug into the igloo and all I saw were two aspen chips stained with blood. I don't know who bled but they both seem healthy. I checked both of them and there were no stains of blood or anything. I noticed the female's genitals seemed wet, if that says anything.

I don't know what this is and I don't know if it was the male being too forceful when he tried to go at her or if this is some internal bleeding. I'll check tomorrow to see if there's more but there's not too much.

Thanks. (All my mice are albino feeder mice)